Microsleep

A microsleep is an episode of sleep lasting from a fraction of a second up to several seconds. It often occurs as a result of a sleep debt, sleep deprivation, or mental fatigue, sleep apnea, narcolepsy, hypersomnia, etc. Microsleeps (or microsleep episodes) become extremely dangerous when occurring during situations which demand continual alertness, such as driving a motor vehicle or working with heavy machinery. People who experience microsleeps usually remain unaware of them, instead believing themselves to have been awake the whole time, or feeling a sensation of 'spacing out'.

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.