Blackout – was it a fit or a faint?

People generally experience a blackout (temporary loss of consciousness) from one of two common problems: (1) Insufficient blood flow to the brain (syncope)  or (2) Abnormal electrical activity within the brain (seizure).


Syncope (or a faint) is caused by insufficient blood flow to the brain because of low blood pressure.  There may be a prodrome of dizziness loss of vision and hearing weakness, flushing, nausea (sometimes referred to pre-syncope).  Then there will be overt loss of consciousness that leads to the faint.  The affected patient will typically fall by dropping forwards from loss of muscle tone. The affected patient might look pale and clammy, and will usually come around quickly of they are allowed to lay down on floor allowing blood flow to return to the brain.  Syncope can be caused by dehydration, irregular heart beat, or emotion (vasovagal or “neurocardiogenic” syncope).


A seizure (or a “fit”) is caused by abnormal electrical activity in the brain, usually accompanied by a clinical event that can vary from a brief loss of awareness (an absence seizure or “petit mal”) to loss of awareness with thrashing limb movements (a tonic-clonic or grand mal seizure).  A generalized tonic-clonic seizure will usually be associated with increased muscle tone, so the patient will stiffen up and fall backwards not forward and may bite their tongue.  The eyes will be open, and their may be loss of bladder and bowel control.  There may be flailing limb movements that lead to injury.  After the seizure stops, the patient will usually be confused or dazed, and not come around immediately like the syncope patient.


Here is a table that emphasizes the differences between fits (seizures) and faints (syncope):



If you have experienced a blackout, what should you do? A simple faint in an otherwise young healthy person may not need emergent medical care.  However, syncope in an older person with a cardiac history, or syncope associated with chest pain and breathlessness could indicate a heart problem and usually justify an emergency room visit.  Similarly a new onset seizure in somebody not previously know to have epilepsy should justify an emergency room visit.


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