Syncope is a loss of consciousness and postural tone. Although arising suddenly from prolonged recumbency or returning from weightlessness to Earth's gravity can result in syncope from orthostatic or vasovagal effects, there are many other possible causes. These causes can be divided 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 syncope in otherwise healthy individuals. Two of the cases emphasize the usefulness of prolonged combined EEG/EKG monitoring. The categories of loss of consciousness experienced by air crew members are reviewed. The most important screening tool in identifying the mechanism(s) of syncope is a detailed history emphasizing a search for underlying disease, the specific associated circumstances, and pre- and post-event symptoms. The type of diagnostic studies, i.e., cardiac or neurologic, undertaken should be based on the historical data. Seizures must be considered as a possible mechanism of otherwise unexplained loss of consciousness in nonelderly persons, including air crew members.