Syncope is a loss of consciousness and postural tone. Although arising
suddenly from prolonged recumbency or returning from weightlessness t
o Earth's gravity con result in syncope from orthostatic or vasovagal
effects, there are many other possible causes. These causes can be div
ided into several groups. Causes listed in the cardiovascular category
, especially cardiac causes, are more likely to occur in the elderly;
noncardiac causes are more common in the younger population. The cases
described herein illustrate the often unexpected mechanisms of syncop
e in otherwise healthy individuals. Two of the cases emphasize the use
fulness of prolonged combined EEG/EKG monitoring. The categories of lo
ss of consciousness experienced by air crew members are reviewed. The
most important screening tool in identifying the mechanism(s) of synco
pe is a detailed history emphasizing a search for underlying disease,
the specific associated circumstances, and pre- and post-event symptom
s. The type of diagnostic studies, i.e., cardiac or neurologic, undert
aken should be based on the historical data. Seizures must be consider
ed as a possible mechanism of otherwise unexplained loss of consciousn
ess in nonelderly persons, including air crew members.