What Caused This Woman to Faint?

 Dear Dr. Brayer;

My mother, age 66, fainted while she was at work.  She was taken to the emergency room and was evaluated for hours, including a CT scan of her head.  They could not find a reason and sent her home.  Could it have been a stroke that didn't show up?  
Thanks, Heidi

Dear Heidi,
The medical term for fainting or sudden loss of consciousness is syncope.  It occurs when the blood flow to the brain is not adequate to supply oxygen and glucose and fainting can occur after only 5 seconds of hypoperfusion.   It is actually pretty common and even after careful evaluation, no cause can be found in 60% of cases.

It would be rare for a stroke to cause syncope and they do not usually go together.  A patient might have a brain hemorrhage that would cause a severe headache followed by a loss of consciousness, but that is different from a simple faint and those patients do not spontaneously wake up.  Strokes usually cause sudden weakness on one side of the body or face and a severe stroke can cause a coma but the patient does not spontaneously wake up a few minutes later as they do with fainting.

The most common cause of syncope is from emotional stress, pain or standing too quickly with pooling of the blood in the lower legs.  It is common for soldiers standing at attention to faint for the same reason.  Dehydration or exhaustion can also cause syncope.  One type of syncope in men is called "micturation syncope" where they faint with urination. The cause is unknown but it usually happens at night after a deep sleep.

More  serious causes are from irregularities of the heart or a seizure.  These conditions can be found with a good history, understanding the events before and after the syncopal episode, physical exam and cardiac tests. 

The majority of children and healthy adults have no structural heart disease to account for fainting.