Passing Out / Amnesia — Full Text

What do we when a patient comes to us saying they “passed out,” usually sometime recently? Or the “lost time,” a period which they can’t recall anything? Today they look perfectly well, act completely normally.  We perform a good physical exam, focusing on the heart and the neurologic system (for the brain), but if they’re fine today, everything is invariably normal.

Our diagnosis will be made entirely by history.  We’ll order tests based on the history, but they may also be normal.  Below, we use the abbreviation LOC (Loss of Consciousness).

The work-up for a patient actively confused, seizing, or in a coma, is extensive.  I learned the mnemonic “Vowel TIPS”, which is how E.R. providers orient their thought diagnostic process.  But for the person who had a “spell” or “episode” that’s over & done with, and now feels fine, possibilities are much more limited.  This is our current topic.

Causes of Loss of Consciousness (LOC)

…………..Patient Fell to Floor  
Faint (a.k.a. Syncope)
Seizure (generalized)
Transient Ischemic Attack (TIA)
Concussion  (from Head Trauma)
Conversion Reaction
……….Episode of Amnesia (without Fall)  
Complex-Partial Seizure
Dissociative State
Transient Global Amnesia


Diagnosis in a Nutshell

1.  Our diagnosis will be made entirely by taking a good history.

  • After deducing the likely condition, we order tests to better understand it
  • Tests are often normal

2.  If a person fell to the ground unconscious, it was most probably a Faint or a Seizure

3.  If a Faint, we distinguish between a Non-Dangerous Faint, or one due to Heart Disease


Witnesses are obviously especially helpful.  If they didn’t accompany the patient to our office, we call them.  If the patient doesn’t know how to reach them, we have them try to find out & let us know tomorrow.  We query witnesses systematically to rule-out or rule-in the above conditions.  We use the abbreviation LOC (Loss of Consciousness).

Patient Fell to the Ground

Faint (medical term is “Syncope”) – see link for different types (some can be very dangerous)

  • Sudden momentary drop of blood circulation to the brain
  • Lasts less than 30 seconds (very rarely longer)
  • Patient regains consciousness immediately; may feel sleepy or fatigued a few minutes, but is alert & thinking normally
  • There may be a trigger, like the sight of blood (see link)
  • Suspect due to heart disease if occurs during exertion, there are risk factors for heart disease, or family history of sudden death
  • A Faint may include very brief shaking resembling a Seizure
  • Head trauma caused by the faint (fell & hit head) may confuse things greatly (rare)

Seizure —  Generalized (a.k.a. “Grand Mal”, “tonic-clonic”)

  • Nerve transmission in brain goes haywire; massive short circuits
  • Lasts 20-90 seconds usually, but can go on and on
  • Symmetrical shaking movements, both arms & legs
  • Face may turn blue
  • May foam at mouth, eyes may move abnormally
  • May bite tongue, may be incontinent of urine / stool
  • Patient recovers alertness gradually, usually takes 15-30 minutes
  • Patient has no memory of what occurred during the event
  • May sense an aura: weird feeling / movement just before the seizure

Concussion  (from Head Trauma)

  • Witnesses say the LOC occurred immediately with the trauma (as opposed to fainting first, & hitting head with fall)

Transient Ischemic Attack (TIA)  —  from Basilar Artery territory (back of brain)

  • Start of a stroke, that resolves quickly on its own
  • Patient may recall severe vertigo (room-spinning)
  • Maybe previous episodes of basilar artery disease: vertigo, double-vision, slurred speech, problem swallowing saliva, imbalance, partial blindness, half of face / body goes numb
  • Risk Factors for Stroke (same ones for Heart Disease which causes Fainting)

Hyperventilation  —  very fast breathing from Anxiety

  • Witnesses describe reason for anxiety, maybe note there was rapid breathing immediately beforehand
  • Patient recalls feeling dizzy (not vertigo), tingling of lips / hands
  • LOC lasts briefly (unless Conversion Reaction follows, see below)
  • In clinic we may listen to lungs while patient breathes hard & fast, which may provoke the dizziness / tingling

Conversion Reaction  —  Psychological “escape” from an intolerable situation (see link)

  • Can last any period of time
  • Any “jerking” movements are random, not symmetrical or consistent
  • Patient squeezes eyes shut, or cries (cannot occur with a seizure)
  • Bites tip of tongue, or lip (with seizure, it’s side of tongue)
  • Level of consciousness may fluctuate, come & go
  • Patient had some awareness of environment during the episode, can describe what people did or said (with Seizure there’s complete amnesia)
  • The LOC comes & goes

Intoxication  —  With witnesses, the diagnosis is easy.  If from poisoning, may be hard

Patient Did Not Fall  (see Explanations below)

Seizure  —  Complex-Partial, without generalization (no “Grand-Mal”)

  • Seizure in only one part of the brain (usually temporal lobe)
  • Begins with staring; smacks lips / grimaces
  • May include a variety of behaviors / utterings (see link)
  • Doesn’t respond (loss of awareness), with complete amnesia for the event
  • May last up to 4 minutes; may come out of it quickly or even 1-2 hours

Dissociative State  —  Psychological reaction to intolerable traumatic memories

  • The form relevant here is by definition temporary; some forms can be long-lasting
  • Almost always occurs without witnesses, when patient is alone
  • Loss of awareness, doesn’t respond appropriately to stimuli
  • Period of amnesia may last hours
  • If witnesses present, they may describe outbursts or strange moods

Transient Global Amnesia

  • Identified in 1956, cause unknown
  • Age >50 years-old, usually older
  • Lasts 1-10 hours
  • Patient is confused: knows own name, but asks repeated questions
  • May have memories of past events, usually not the recent past
  • No LOC: is aware of things happening around them
  • Able to perform complex tasks like drive, cook, play piano, etc.

Some Explanations:

Complex-Partial Seizure —  a true neurologic event in the brain, with abnormalities on electroencephalogram (EEG).  Synonyms in the past included “Psychomotor” and “Temporal Lobe” seizures / epilepsy.  If it happens to “generalize,” there’s a fall to the ground with shaking, etc. (a.k.a. “Grand Mal seizure”), but often that doesn’t happen.  Rather, the patient does weird things like make strange facial movements, keep repeating words, even walking around or undressing.  It lasts several minutes; the patient may come out of it quickly or slowly (up to 2 hours)  There’s complete amnesia for what happened.

Franklin was a blind AIDS patient with complex-partial seizures, which he described as episodes of complete amnesia.  At one visit, he commented he’d just had one, on the way to the clinic with his health worker.  So I asked the health worker, “What happened?  What did you talk about?”  He replied, “Nothing.  Billy was in his own mood, just mumbled, didn’t feel like talking.”   The health worker had actually accompanied a patient in the midst of a seizure, & didn’t realize it!

Dissociative State —  a person loses awareness due to psychiatric mechanisms that preoccupy them with inescapable thoughts, which are usually trauma-related (PTSD).  They “trance-out,” become unresponsive, and have amnesia for the episode.  When temporary (some forms can be long-lasting), it usually occurs when the person is alone, thus not distracted.  See the movie Primal Fear with Richard Gere, Edward Norton, Laura Linney [not my top pick of cinema but quite entertaining; R-rated, may offend some devoutly religious].

Transient Global Amnesia (TGA)  —  A newly-recognized (1956) syndrome in which a person over 50 years-old (usually older) suddenly becomes unable to form new memories, so they can’t understand what’s going on from moment to moment.  They know who they are, and can recall some distant memories, but not recent ones, so they are profoundly disoriented as to what is occurring to them, and ask questions repeatedly. 

TGA lasts less than a day, and usually doesn’t recur.  Medical scientists have been unable to define its cause (may be neurologic, cardiovascular, or psychological).  TGA is usually so blatant and concerning to anyone in contact with the person, that they’re taken to an emergency room.

Conversion Reaction —  The mind’s way to escape an intolerable situation, by subconsciously doing something that winds up forcing the person out.  If it involves falling with “LOC,” it’s now called “Psychogenic Non-Epileptic Seizure,” instead of previous less-friendly names like “pseudo-seizure” or “hysterical seizure.”  It isn’t “faking it,” because there’s no conscious control. 

In a generalized seizure, there is complete loss of awareness during the event, & also during the 15-30 minutes it takes to recover.  For amnesia & LOC to alternate on-and-off with normal thought is not possible with true neurologic brain disease [so we would think Conversion Reaction].  Of course, a person can seize, begin to recover, then seize again.  This qualifies as Status Epilepticus, but is life-threatening, pretty rare, & highly unlikely to have resolved on its own.

See the link for some interesting examples of Conversion Reactions.


Often there are no witnesses.  A patient describes an episode of amnesia several days ago.  Maybe they awoke on the floor, maybe not; they just don’t remember what happened.  This is harder.

If they awoke on the floor, the causes may be:

The last five are unlikely.  Concussion from head trauma without memory of the blow is possible but highly doubtful; at least, the head would feel sore.  We’d only consider a basilar artery TIA if it recurred, or if a patient recalled severe vertigo initially.  Transient Global Amnesia usually lasts long enough for the person to interact with others, who’d be very concerned and take them to an ER.  Collapse from a Conversion Reaction only occurs if others are around (who provoked the stress).  Diagnosing Intoxication requires patient insight and honesty.

So we’re usually left with Seizure vs. Fainting, & nobody to describe how long it lasted.  The diagnostic approaches are very different.  We obtain clues from the little history we have.  Most important, we try to get a sense of how much time elapsed, asking about the last thing they remembered before, & the first thing afterward.  If the event occurred in a busy public area, it’s unlikely to have lasted more than a few minutes before someone would call for help (thus a Faint, not seizure).

For example, one of my patients fell in the bathroom.  A family member heard the thud, ran in, & the patient was already awake.  Time here was clearly short.  No tongue bite or incontinence.  Diagnosis: Faint (probably caused by reflex slowing of the heart from the Vagus Nerve, which also controls urination; so some people faint when they pee).

People who faint retain memories up to the point they lose consciousness.  But they don’t remember the fall.  Someone who trips, hits their head, and is knocked out, may recall going down.  But if not, it’s much harder to know, unless hand injury shows they had tried to protect themselves with their hands.

Another patient awoke on the floor by her bed.  Could have fainted from sudden standing (orthostatic syncope), but then she’d have remembered losing consciousness right after arising.  Her inability to describe a rapid coming-to suggested a longer time course (post-ictal phase after a seizure).  Diagnosis: Seizure (which may occur disproportionately at night).

Epileptic seizures often have auras which might be recalled.  They include a wide variety of phenomena, depending on the part of the brain where it all began.  Click for a list of possible auras.

If there was No Fall, just a period of unwitnessed amnesia for less than an hour, the possibilities are:

Transient Global Amnesia (see above) lasts over an hour, maybe up to 10 hours.  A Dissociative episode can be ongoing, but eventually the person would interact with others and come out of it.

I once worked-up a friend who’d been working abroad during a civil war, and was having episodes of amnesia.  She visited San Francisco, I ordered an EEG and MRI to rule out Seizure (both were normal).  A consulting Neurologist said there was no way to distinguish between the 2 conditions, leaned toward the latter since tests were normal & war is tough.  But I knew her situation abroad, which wasn’t particularly traumatic or dangerous.  It was only weeks later, before flying to Chicago, that she confided she was about to confront a brother who’d molested her in childhood.  Diagnosis: Dissociative Episodes.

Diagnostic Tests for Loss of Consciousness

We order tests and refer to specialists depending on the reason we think a person had lost consciousness.  This depends entirely on the medical history we’ve obtained.  Again, this is in the context of the event having occurred some time ago, and the person feels perfectly fine today.

The main tests available which we might consider include:

We never order all of these, which are described below.  Rather, we order those most appropriate based on our History, which identifies the most likely Cause:

Faint (Syncope)

Whether or not we do any tests depends on the reason we think they fainted (see link for more discussion):

Vasovagal Syncope – the most common cause of fainting.  We’d be convinced if there’s a clear history (e.g. fainted at sight of blood; in a hot crowded room; right after urinating, etc.).  The patient often feels woozy or nausea right before.

  • Further testing is not necessary, as long as we’re sure it’s not due to heart diseases (see below).
  • We just explain, and reassure the patient there’s nothing serious.

Orthostatic Syncope  —  Occurs immediately after standing up (usually from lying down, maybe from sitting).  We suspect this if the person was dehydrated, or just began a new medicine with fainting as a possible side effect.  Long-standing Diabetes, Parkinson’s, and other diseases can cause this.

  • If patient still feels any symptoms upon standing, we check their Postural Vital Signs (heart rate and blood pressure while lying down, & then after standing abruptly; see link for explanation).
  • Treatment is mainly warning patient to get up slowly

Heart Arrhythmia  —  There are various kinds of abnormal heart rhythms that can cause fainting.  Some can be serious, even life-threatening (see link).  We suspect an Arrhythmia if the patient faints without any warning symptoms like dizziness or nausea.  We order the following tests (see Arrhythmias for more explanation):

  • EKG.  Usually normal if no symptoms at the time, but rarely there are clues to uncommon causes.
  • Ambulatory EKG, i.e. portable.  Worn on a belt if done for 24-48 hours; a patch on the chest if for 2-4 weeks (showering is OK).
  • Implantable recorder, if recurrent faints and the above tests are normal

Other Heart Disease  —  We especially suspect this if fainting occurs during exertion.  There may also be symptoms like chest pain, shortness of breath, nausea, or burst of cold sweat which occur just beforehand.  Two types of heart disease may cause fainting with exertion:

  • Coronary Artery Disease (causes Heart Attacks)
  • Cardiac Outflow Obstructions that interfere with blood as it’s pumped out of the heart (tumors, heart valve disease, abnormal muscle growth)
  • See also The Heart – Anatomy (with diagrams)

To diagnose Coronary Artery Disease, we obtain an EKG, order Stress Tests, maybe refer for cardiac catheterization (see link).

To diagnose Cardiac Outflow Obstructions, we obtain an Echocardiogram.

Abnormal Neck Anatomy  —  This is very rare, but if someone faints only when they turn their head a certain way, we’d order an Angiogram by MRI or CT, and/or perhaps refer to a Vascular specialist.

Tilt Table Testing as noted above: what’s this?  The patient is strapped to a table, abruptly raised from supine to upright, and held there (maybe for over 30 minutes).  If a faint occurs, it diagnoses Vasovagal Syncope.  The problem is that false-positives and false-negatives are common, and accuracy is low.  I’ve never had it performed on a patient, much less ever ordered it.

It might be useful for the older patient with risks for heart disease but a completely negative cardiac work-up, if we want some reassurance that frequent faints were in fact vasovagal.  Other indications include frequent unexplained falls, to prove any shaking movements are in fact from faints (vs. seizure), & maybe for fainting in a person with a high-risk occupation (pilot, acrobat, etc.).


Generalized Seizure (a.k.a. “Grand Mal”) causes the classic fall to floor, body shakes, foams at mouth.  Complex-Partial Seizure begins with weird facial movements, then a trance during which a patient may still walk and mumble.  The patient has complete amnesia for the event.  We order the same tests no matter what kind of seizure we suspect may have occurred.

  • MRI of Brain  —  This won’t show if there’s a seizure, but will find a tumor if one exists.  A CT scan is able to find masses large enough to cause headaches, but for a tiny tumor capable of causing a seizure, we need the MRI.  Both MRI and CT can find a Subdural Hematoma (blood clot in the brain from a prior fall), which can cause seizures later on.
  • Electroencephalogram (EEG)  —  Scalp electrodes used to detect abnormal brain waves, to diagnose a seizure predisposition.  It’s best if the patient is sleep-deprived before the test.
  • CBC and CMP, common simple blood tests which may reveal an underlying illness

An EEG is always abnormal during an actual seizure, but may be normal at other times.  This is especially so with a Complex-Partial Seizures, because the abnormal electrical discharges may come from deep in the brain.  If seizures are frequent enough, Neurologists may admit a person to the hospital for 3 days to perform a continuous EEG while video-recording the patient.  In rare cases an EEG may be done surgically, placing electrodes deep in the temporal lobe.

Transient Ischemic Attack (TIA)

This is the start of a Stroke, but the patient recovers fully.  It’s not a common cause of having passed out, but one to think of if a person has risks for Atherosclerosis.  This type of TIA would come from the brain’s basilar artery, which might also cause vertigo, double vision, slurred speech, or trouble swallowing saliva.  If we suspect a TIA, we’d order:

  • MRI of Brain  —  To make sure the patient didn’t have a full stroke
  • Angiogram by MRI or by CT, of both the Head and also the Neck, to look for abnormal arteries which can cause a stroke
  • Echocardiogram to look for clots in the heart which can be swept to the brain
  • EKG, Ambulatory EKG, to look for Atrial Fibrillation which can cause clots in the heart

Other Causes of Passing Out

Other entities in the table are suspected and diagnosed by history alone; there are no useful supportive tests.  Transient Global Amnesia, as noted, is so startling that patients are invariably transported to an E.R.  If all tests there are normal (see the mnemonic Vowel-TIPS for diseases causing abnormal mental status at the moment), the patient is observed until they recover.

Dissociative episodes, psychological escape mechanisms for avoiding intolerable traumatic thoughts, can be impossible to distinguish clinically from Complex-Partial Seizures (due to physical abnormalities in the brain).  We commonly order an EEG and MRI, with subsequent referral to a Neurologist, to reassure both patient and ourselves.  There are recent 72-hour ambulatory (portable) EEGs which may be available.  Up to 40% of patients hospitalized for 3-day EEG plus video-recording are diagnosed to have a psychiatric cause of their episodes.

That’s all for “Passing Out”  —  we hope you’ve retained consciousness while reading all this.

See also Passing Out for the clinician’s condensed thought-process when face-to-face with a patient.

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