Syncope or Seizure? How to Approach Sudden Loss of Consciousness in the Emergency Room

Someone suddenly collapses in front of you—can you tell if it’s syncope, a seizure, or a stroke? While all may present as a transient loss of consciousness (TLOC), the underlying causes vary widely, from benign reflex syncope to life-threatening cardiac or neurological disorders. This article provides a clear and structured approach to help medical students and junior doctors differentiate causes of TLOC and respond effectively in real clinical settings.

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📚 What You Will Learn from This Article

• Understand the difference between syncope and transient loss of consciousness (TLOC)
• Identify red flag signs that require urgent evaluation
• Prioritize your differential diagnosis and initial approach in emergency and outpatient settings

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🩺 Case Introduction: A Man Who Collapsed on His Way to Work

🚪 Doorway Information

• Age/Gender: 55-year-old male
• Chief Complaint: Collapsed on a train station platform
• Vital Signs: BP 112/68 mmHg, HR 58 bpm, RR 14/min, SpO₂ 98% (room air), Temp 36.7℃

“I was walking on the station platform when everything suddenly went black.
Next thing I knew, I was surrounded by paramedics.
It couldn’t have lasted more than a minute. I didn’t feel any chest pain or shortness of breath.
I’ve had occasional lightheadedness before, but I’ve never actually passed out like this.”

What would you do if this patient collapsed right in front of you on the street—or was rushed into your ER without warning?

Before anything else, the key question is: “Is this an emergency, or is observation enough?”

You want to think carefully, but in real-time situations, you’ll often need to act quickly.

That’s why we’ll begin by reviewing the basic distinguishing points between different causes of loss of consciousness.

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🧭 How Should You Think? — First Impression & Diagnostic Approach

Not all transient loss of consciousness (TLOC) is syncope—this is the first and most important point to remember.

TLOC refers to a sudden, short-duration, and spontaneously resolved loss of consciousness. It includes a wide variety of conditions with very different causes and levels of urgency.

🔍 Classification of TLOC

Category	Underlying Mechanism	Common Examples
1. Syncope	Transient cerebral hypoperfusion	Reflex syncope, orthostatic hypotension, cardiac syncope
2. Non-syncope TLOC	Neurological, metabolic, toxic causes	Seizure, hypoglycemia, hyperventilation, psychiatric causes, stroke (AIUEO TIPS)
3. Traumatic TLOC	Head injury-related	Concussion, sports injuries, falls

💡 Why Focus on Syncope?

Among all causes of TLOC, syncope is the most common—and also the one that can hide life-threatening pathology, especially cardiac causes.
That’s why evaluating syncope first and quickly excluding red flags is a high-priority step in emergency settings.

🧠 Tips: Not All TLOC Is Syncope – Broaden Your Differential with AIUEO TIPS

While syncope is the most common cause of transient loss of consciousness (TLOC), many other potentially serious conditions can mimic it.
The AIUEO TIPS mnemonic helps you remember the wide range of possible causes:

Letter	Category	Examples
A	Alcohol / Acid-base	Alcohol intoxication, metabolic acidosis
I	Insulin	Hypoglycemia, diabetic ketoacidosis
U	Uremia	Renal failure, hepatic encephalopathy
E	Electrolytes / Encephalopathy	Hyponatremia, hypercalcemia, meningitis
O	Oxygen / Overdose	Hypoxia, CO poisoning, drug overdose
T	Trauma / Temperature	Head injury, heatstroke, hypothermia
I	Infection	Sepsis, meningitis, encephalitis
P	Psychiatric	Delirium, dissociation, severe depression
S	Seizure	Postictal state, non-convulsive seizure

Whenever syncope doesn’t fully explain the clinical picture, use this checklist to ensure you don’t miss a critical alternative diagnosis.

🌀 Not sure how to distinguish between presyncope (feeling faint) and other causes of dizziness? Check out our article:
🧭 Clinical Approach to Dizziness: Vertigo, Presyncope, and More

⚡️ Want to dive deeper into seizures and epileptic events as a cause of TLOC? Read more here:
⚡ Clinical Guide to Seizures and Convulsive Disorders

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🧠 Fact / Problem / Hypothesis

In real-life situations, staying calm and breaking down the case systematically leads to more accurate diagnosis.
Let’s begin by organizing the information from our patient using this clinical reasoning framework:

🔎 Fact (What the patient tells us)

• 55-year-old male collapsed on a train station platform while commuting
• Reports sudden blackout — “everything went dark”
• No chest pain, dyspnea, headache, or weakness before or after the episode
• Recovered spontaneously within about a minute
• No significant past medical history, though occasional lightheadedness in the past

🧩 Problem (Reframing with semantic qualifiers)

• First episode of transient loss of consciousness (TLOC)
• Short duration, complete spontaneous recovery, no focal neurological deficits
• Minimal warning signs; occurred while walking (mild exertion)
• No signs of dehydration, infection, or diabetes

➡️ These features point toward syncope rather than seizure or metabolic causes.
However, the lack of prodrome and exertional setting raise concern for a cardiac etiology.

🧠 Hypothesis (Differential based on the 3 types of syncope)

1. Reflex syncope (vasovagal, situational): No clear trigger like prolonged standing or urination; mild prodrome (nausea, cold sweat) may suggest susceptibility to autonomic response
2. Orthostatic hypotension: Less likely since episode occurred during walking, not immediately after standing; but history of lightheadedness and unknown medication history still warrant consideration
3. Cardiac syncope: Most concerning. Sudden onset during activity, no prodrome, and rapid recovery → must rule out arrhythmia, valvular disease (AS, HCM), Brugada, etc.

🧾 Conclusion: The clinical priority is to rule out cardiac syncope first. Physical exam and ECG are essential next steps.

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🗣️ Step 1: History Taking – Structure and Key Questions

In cases of syncope and altered consciousness, history-taking is often the most critical diagnostic tool.
Because patients are unconscious during the event, it’s essential to combine their recall with eyewitness accounts.

📌 Use OPQRST to Understand the Timeline of the Episode

• O – Onset: Was it sudden or gradual? What were they doing at the time (e.g., standing, urinating, exercising)?
• P – Provocation: Any triggers like pain, prolonged standing, coughing, emotional stress, urination, alcohol?
• Q – Quality: How did the loss of consciousness feel? “Everything went black”? “Felt dizzy”? “Blanked out”?
• R – Radiation: Uncommon, but assess for pain that may point to cardiac causes (e.g., chest pain radiating to arm)
• S – Severity: Did they fully collapse or just feel faint and sit down?
• T – Time Course: Duration of LOC and time to recovery? Was there confusion afterward?

👀 Eyewitness reports (skin color, body movements, breathing patterns, snoring, incontinence) are invaluable in identifying seizure vs syncope.

🔎 Explore Risks with the PAM HITS FOSS Framework

Even a seemingly benign episode can have a dangerous underlying cause. Use the following checklist:

• P: Previous medical history (heart disease, arrhythmias, stroke, epilepsy)
• A: Allergies (especially to drugs that may prolong QT)
• M: Medications (antihypertensives, diuretics, antiarrhythmics, psychiatric drugs)
• H: Hospitalizations (previous admissions for syncope?)
• I: Injuries (head trauma, fractures from falls)
• T: Surgeries (cardiac surgery, electrolyte-related complications)
• S: Psychiatric history (panic, dissociation)
• F: Family history (sudden death, HCM, Brugada, long QT, epilepsy)
• O: OBGYN history (anemia, early pregnancy-related hypotension)
• S: Sexual history (infection risk, HIV, syphilis-related CNS involvement)
• S: Social habits (alcohol, smoking, drugs, sleep, diet, stress)

💡 Red Flag Screening – Ask These Critical Questions

• “Did you collapse during exercise?” → Think cardiac syncope
• “Did you feel chest pain or shortness of breath?” → Consider ACS, PE
• “Did you have any warning signs like nausea or cold sweat?” → Suggests reflex syncope
• “Have you had similar episodes before?” → May point to psychiatric or reflex causes
• “Have you recently changed or missed any medications?” → Risk of orthostatic hypotension
• “Did you eat breakfast? Were you in a hot place?” → Environmental stress and dehydration

🧩 Column: When a Patient Says “I Just Blacked Out”

Patients often report, “Everything went black,” or “I was on the ground before I knew it.”
This doesn’t mean there was no prodrome—it may have simply gone unnoticed.
Ask: “Just before it happened, did you feel nauseous, sweaty, or uncomfortable?”
These subtle clues may point toward reflex syncope.

🧩 Column: Don’t Miss Central Nervous System Causes

Some strokes (e.g., brainstem infarcts) or subarachnoid hemorrhage (SAH) may initially look like syncope.
While rare, they must be ruled out if the patient reports:

• Sudden severe headache (“thunderclap headache”)
• Seizure-like movements, vomiting, or neck stiffness
• Prolonged confusion or delayed recovery

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🩺 Step 2: Physical Examination – Identify Red Flags and Clues

Even if the initial impression suggests syncope, we must not let our guard down.
The key is to determine whether this is truly a benign event—or a dangerous neurological or cardiac emergency hiding in plain sight.

🧠 Assess Level of Consciousness

• JCS or GCS: Use GCS internationally (JCS in Japan)
• Alert (A): Fully responsive and oriented
• Lethargy: Responds to verbal stimuli but drowsy
• Stupor: Responds only to painful stimuli
• Coma: No response to any stimuli

💡 Pearl: Rapid onset, short duration, and complete recovery → more likely syncope.
Ask: “Were you able to speak normally right after regaining consciousness?”

🔍 General Observation – Look for Clues

• Vital Signs: BP, HR, RR, SpO₂, temperature — always check!
• Skin: Cyanosis, pallor, diaphoresis, trauma, petechiae, signs of dehydration
• Breathing: Kussmaul (metabolic acidosis), Cheyne-Stokes, apnea
• Pupils: Size, reactivity; pinpoint (opioids), dilated (anticholinergics)
• Neurological: Motor deficits, speech disturbance, neck stiffness, Babinski sign

🔎 Physical Signs by Syncope Type

• Reflex syncope: Pale face, cold sweat, bradycardia, possible incontinence
• Orthostatic hypotension: ≥20 mmHg SBP drop or HR increase upon standing; dry mucous membranes, poor skin turgor
• Cardiac syncope: Sudden LOC, irregular rhythm, murmurs (AS, HCM), chest tenderness

⚡ Seizure vs Syncope – Watch for These Signs

• Tongue biting, incontinence, postictal confusion → suggest seizure
• But be cautious: these can occasionally appear in syncopal events too

🩻 Use POCUS to Rapidly Rule In/Out Critical Causes

• IVC collapse: Suggests hypovolemia
• Cardiac tamponade: RA collapse, paradoxical septal motion
• B-lines: Pulmonary edema (heart failure or volume overload)
• Free fluid in Morrison’s/Douglas pouch: Internal bleeding from trauma

🧩 Column: How to Apply Pain Stimuli Safely

To assess response in reduced consciousness, use safe techniques like rubbing the sternum, pressing the nail bed, or pinching the trapezius.

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🔬 Step 3: Tests and Imaging – Targeted Workup Based on Hypotheses

In syncope or altered mental status, testing should never be random.
Let the story and physical exam guide your next step—each test should answer a specific diagnostic question.

📈 ECG – Always First to Rule Out Cardiac Syncope

Cardiac syncope can be fatal. An ECG can literally save a life.

• Bradyarrhythmias: Sick sinus syndrome, AV block
• Tachyarrhythmias: VT, WPW syndrome
• Hereditary channelopathies: Brugada, long QT syndrome (especially in young patients)

🚩 Red Flag Examples: “Collapsed during exertion,” “No prodrome” → Do an ECG immediately.

🧪 Blood Tests – Assess for Metabolic and Toxic Causes

• Glucose: Hypoglycemia can cause coma or seizure-like episodes
• Electrolytes: Na, K, Ca — can affect consciousness and ECG
• Renal/Liver function: Rule out uremia or hepatic encephalopathy
• CRP, WBC: Suspected infection, sepsis, or meningitis
• Ammonia, Lactate: Suspect metabolic encephalopathy or shock states

🧠 Head CT / MRI – Order Only When Justified

Head imaging is not always needed for every altered mental status.
Use it wisely and with purpose:

• Suspected SAH: Sudden severe headache, vomiting, neck stiffness, LOC
• Focal neurological deficits: Paralysis, aphasia, gaze deviation
• Trauma history or anticoagulant use: Even minor falls may lead to bleeding

❗ Note: Normal CT doesn’t rule out all dangerous conditions like hypoglycemia, overdose, or infection.

🧠 Clinical Flow for Workup

• Red flags present? → Start with ECG and basic labs
• Suggestive of reflex or orthostatic syncope? → Minimal additional tests
• Concern for stroke, encephalitis, trauma? → Proceed with imaging as needed

🧩 Column: “Just in Case” Head CT? Think Twice.

Ordering a CT “just in case” can lead to false reassurance or delay in real diagnosis.
Ask yourself: “What am I trying to rule out?”
Tests should serve a purpose—not a reflex.

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🌀 Let’s Revisit the Case – Apply the Steps

Now that we’ve reviewed Steps 1 to 3 of our diagnostic approach,
let’s go back to our original case and walk through each step as if we were at the bedside.

🗣️ Step 1: History Taking

Doctor: “What brings you in today?”
Patient: “This morning I was walking on the station platform, and suddenly everything went black.
When I came to, paramedics were around me.”

Doctor: “Did you feel anything just before it happened?”
Patient: “I felt a bit nauseous and sweaty, like I couldn’t keep standing.”

Doctor: “Have you ever had anything like this before?”
Patient: “I’ve had lightheadedness from time to time, but never actually collapsed.”

Doctor: “Any history of heart disease or sudden death in the family?”
Patient: “No, nothing like that.”

(thinking): Hmm… Prodrome, upright posture, and bradycardia. Reflex syncope seems likely,
but I’d still want to rule out cardiac causes, especially given his age.

Fact: Sudden loss of consciousness while walking; brief duration; spontaneous recovery.
Mild prodrome (nausea, sweating). No seizure-like features.

Problem: TLOC with short duration, no confusion, no focal signs → consistent with syncope.

Hypothesis:

• Reflex syncope (vasovagal)
• Orthostatic hypotension (needs medication review)
• Cardiac syncope (still needs to be excluded)

🩺 Step 2: Physical Examination

(thinking): He’s alert (GCS 15), slightly pale, moist skin. No neurologic deficits.

• Vitals: BP 112/68 mmHg, HR 58/min, RR 14/min, SpO₂ 98%
• Heart: Regular rhythm, no murmurs or JVD
• Lungs: Clear bilaterally
• Neuro: No focal findings; pupils normal

Doctor: “Do you feel dizzy when standing up?”
Patient: “A little lightheaded, yes.”

(thinking): Mild orthostatic component could be present,
but I don’t see any immediate red flags. So far, no signs of stroke or cardiac instability.

🔬 Step 3: Tests and Imaging

• ECG: Normal sinus rhythm, QTc normal, no ST/T changes
• Glucose: 92 mg/dL (normal)
• Electrolytes: Na 134, K 4.1 (mild hyponatremia)
• Other labs: Renal/liver function normal; CRP negative

(thinking): No significant metabolic or cardiac abnormalities.
Normal ECG reassures me that arrhythmic causes are less likely.

🧾 Conclusion: The most likely diagnosis is reflex syncope with possible mild orthostatic component.
No clear red flags identified. The patient was advised on lifestyle modifications, hydration, and close follow-up.

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📨 When to Refer to a Specialist – Recognizing Red Flags

Not all patients with syncope or TLOC need referral or advanced workup.
But missing a serious underlying cause can be catastrophic.
Here are the key red flags that should prompt urgent referral to cardiology, neurology, or emergency services:

🚩 Red Flags That Warrant Specialist Referral

• Collapse during exertion → Think cardiac syncope
• No warning signs before the episode → Consider lethal arrhythmias, long QT, HCM
• Known heart disease or family history of sudden death (e.g., Brugada, LQTS)
• Recurrent episodes of syncope over a short time
• Prolonged confusion or residual neurological symptoms after recovery
• Significant trauma, especially head injury, from the fall

🧪 Basic Workup Before Referral (Helps Guide Triage)

• 12-lead ECG → Rule out arrhythmias, QT prolongation, Brugada, etc.
• Basic labs: glucose, electrolytes, CRP → Rule out metabolic and infectious causes
• Orthostatic BP test → If orthostatic syncope is suspected
• Head CT → Only if neurological symptoms or trauma is present

📝 Referral Note Should Include: Circumstances of the episode, duration of LOC, recovery details,
presence/absence of red flags, and results of initial tests.

⚽ Sports-Related TLOC: Don’t Miss Concussion

In contact sports like rugby or football, transient LOC may indicate concussion.
Even if the patient regains consciousness quickly, they may have lingering symptoms such as:

• Fatigue
• Headache
• Memory disturbance or confusion

Patients should avoid driving or exercising for 6–24 hours and undergo stepwise assessment before returning to play.

👵 Acute Confusion in the Elderly? Think Delirium

In elderly patients, sudden confusion or altered behavior may be due to delirium rather than syncope.

Common triggers include:

• Infections (UTI, pneumonia)
• Medications (benzos, anticholinergics)
• Constipation, dehydration, sleep disruption

Delirium often requires referral to neurology or psychiatry and a comprehensive medication/environmental review.

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💡 Tips for Clinical Practice – History & Physical Exam

Syncope and TLOC cases are often decided based on history and physical exam alone.
Here are some practical techniques and key observations to improve your clinical reasoning:

🗣️ Useful Questions to Ask

• “Did anyone witness the episode?” → Eyewitnesses can help distinguish seizure vs syncope
• “Were you able to speak normally right afterward?” → Helps differentiate postictal confusion vs syncope
• “Have your medications changed recently?” → Risk for orthostatic hypotension or drug-induced TLOC

🧠 Physical Exam Clues

• Bradycardia + irregular pulse → Possible AV block or sick sinus syndrome
• Check for orthostatic vitals (supine → standing BP and HR)
• Tongue bite or urinary incontinence → May suggest seizure
• Pain response (sternal rub, nail bed pressure) → Safe assessment of consciousness level

📋 Ask Family or Bystanders

• “Did the patient say anything strange before collapsing?”
• “How long was the patient unresponsive?”
• “Did you notice any injury or jerking movements?”

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🗣️ OET Speaking Session – Syncope vs Seizure

👥 Scenario

You are a doctor in the emergency department. A 55-year-old man was brought in by paramedics after briefly losing consciousness while walking on a train platform. He regained consciousness spontaneously within one minute. No chest pain, shortness of breath, or trauma was reported. He has no known past medical history.

You suspect reflex syncope or orthostatic hypotension, but you need to rule out cardiac syncope.

🎯 Your Task

• Explain the possible causes of his episode and why further tests are needed
• Ask about relevant symptoms and risk factors (e.g., cardiac, neurological)
• Reassure the patient and address concerns about fainting or seizures
• Provide information about the initial plan and follow-up if necessary

💬 Sample Statements for Your Task

• “We’re trying to find out whether this was a simple fainting episode or something related to your heart or nervous system.”
• “Have you ever experienced anything like this before? Even just feeling lightheaded?”
• “One of our first steps is to check your heart rhythm and blood pressure.”
• “It’s good news that you recovered quickly, but we still want to rule out any serious causes.”
• “Let’s go through some quick questions about your medications, family history, and lifestyle to help us understand the big picture.”

💬 Common Patient Cues & Sample Doctor Responses

🧠 Challenging Questions & Sample Doctor Responses

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✉️ OET Writing Task – Sample Referral Letter

Today’s Date

Dr. Samantha Lee
Cardiology Department
Central General Hospital

Re: Mr. Kenji Sato, 55 years old

Dear Dr. Lee,

I am referring Mr. Kenji Sato, a 55-year-old male, for further evaluation of a transient loss of consciousness (TLOC) of unclear etiology, with possible cardiac syncope to be ruled out.

Mr. Sato collapsed briefly while walking on a train platform this morning. Eyewitnesses report that he lost consciousness for approximately 30–60 seconds and regained awareness spontaneously without confusion or convulsive activity. He did not report chest pain, dyspnea, or neurological symptoms before or after the event. His vital signs were stable on arrival (BP 112/68, HR 58), and initial ECG showed sinus rhythm without QT prolongation or ST-T changes.

There is no history of cardiovascular disease, seizures, or diabetes. He occasionally experiences lightheadedness, but this is the first episode of syncope. He takes no regular medications and denies any substance use.

Given the absence of prodrome and the occurrence during mild exertion, cardiac syncope cannot be ruled out. I would appreciate your further assessment, including possible Holter monitoring or echocardiography, to ensure safe discharge planning.

Please let me know if any additional information is required.

Yours sincerely,

Dr. [Your Name]
Emergency Physician

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📝 Summary – Key Takeaways and Clinical Mindset

Someone suddenly collapses in front of you—how do you respond?

In this article, we explored how to distinguish syncope from other causes of transient loss of consciousness (TLOC), such as seizures, metabolic disturbances, or stroke.
Using structured frameworks like OPQRST, PAM HITS FOSS, and the 3-type classification of syncope, we learned how to prioritize red flags and build a step-by-step clinical approach.

Key Takeaways:

• Not all TLOC is syncope — consider seizures, intoxication, and intracranial pathology.
• Always rule out cardiac syncope first — it’s potentially fatal but easily missed.
• History and physical exam often provide more value than early imaging or labs.
• Listen carefully to both the patient and any eyewitnesses — they hold the diagnostic clues.
• Use ECG and bedside tests to confirm or exclude life-threatening causes quickly.

Ultimately, the goal isn’t just to assign a diagnosis — it’s to understand why this event happened now, and how to prevent recurrence.

Let’s commit to a clinical practice that is structured, empathetic, and always curious.

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🔗 Related Articles

• 🌀 Dizziness and Presyncope: Clinical Differentiation
• ⚡ Cardiac arrest: ACL & ICLS
• 💤 Fatigue and Tiredness: Diagnostic Approach
• 🚨 Shock and Vital Signs: Recognizing the Red Flags

🌐 Looking for the Japanese version of this article?
👉 【JP】失神と意識障害の診かた：反射性・起立性・心原性の鑑別と緊急対応

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📝 Practice with Mock Cases

Want to apply your knowledge to real-world clinical scenarios? Explore our English-based mock scripts designed for OSCE, USMLE, and OET preparation.

• 👉 Mock Patient Script – Syncope (Fainting, Bradycardia, and Polypharmacy)
  

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📚 References

• Japanese Society for Emergency Medicine. Guidelines for Initial Evaluation of Transient Loss of Consciousness. 2020.
• Japanese Society of Neurology. Epilepsy Clinical Practice Guidelines 2018.
• Brignole M, et al. 2018 ESC Guidelines for the Diagnosis and Management of Syncope. Eur Heart J. 2018;39(21):1883–1948.
• UpToDate: Approach to the adult with syncope in the emergency department.
• Sir William Osler. “Listen to the patient, he is telling you the diagnosis.” – quoted in multiple clinical texts.

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