Microsleep

A microsleep is a period of sleep lasting no more than a few seconds up to a minute. It often occurs as a result of a sleep debt or mental fatigue. Microsleep becomes extremely dangerous when it occurs during situations when continual alertness is demanded, such as driving a motor vehicle. People who experience microsleep usually remain unaware of it, instead believing themselves to have been awake the whole time.

There is little agreement on how best to identify microsleep episodes. Some experts define microsleep according to behavioral criteria (head nods, drooping eyelids, etc.), while others rely on EEG markers, which are known to be weakly correlated with the behavioral features of sleep.