Microsleep

A micro-sleep (MS) is a temporary episode of sleep which may last for a fraction of a second or up to 30 seconds (4-5 seconds according to AAA.com) where an individual fails to respond to some arbitrary sensory input and becomes unconscious. MSs occur when an individual loses awareness and subsequently gains awareness after a brief lapse in consciousness, or when there are sudden shifts between states of wakefulness and sleep. In behavioral terms, MSs manifest as droopy eyes, slow eyelid-closure, and head nodding. In electrical terms, microsleeps are often classified as a shift in electroencephalography (EEG) during which 4–7 Hz (theta wave) activity replaces the waking 8–13 Hz (alpha wave) background rhythm.

MSs often occur as a result of sleep deprivation, though normal non-sleep deprived individuals can also experience MSs during monotonous tasks. Some experts define microsleep according to behavioral criteria (head nods, drooping eyelids, etc.), while others rely on EEG markers. Since there are many ways to detect MSs in a variety of contexts there is little agreement on how best to identify and classify microsleep episodes.

Microsleeps become extremely dangerous when they occur in situations that demand constant alertness, such as driving a motor vehicle or working with heavy machinery. People who experience microsleeps often remain unaware of them, instead believing themselves to have been awake the whole time, or to have temporarily lost focus.

With over 1,550 fatalities and 40,000 nonfatal injuries occurring annually in the United States alone as a result of drowsy driving, sleep loss has become a public health problem. When experiencing microsleeps while driving an automobile, from the perspective of the driver, he or she drives a car, and then suddenly realizes that several seconds have passed by unnoticed. It is not obvious to the driver that he or she was asleep during those missing seconds, although this is in fact what happened. The sleeping driver is at very high risk for having a collision during a microsleep episode.

Historically, many accidents and catastrophes have resulted from microsleep episodes in these circumstances. For example, a microsleep episode is claimed to have been one factor contributing to the Waterfall train disaster in 2003; the driver had a heart attack and the guard who should have reacted to the train's increasing speed is said by his defender to have microslept, thus causing him to be held unaccountable. On May 31, 2009, an Air France plane (Air France Flight 447) carrying 228 people from Brazil to France crashed into the Atlantic Ocean, killing everyone on board. The pilot of the plane reported "I didn't sleep enough last night. One hour – it's not enough," handing over control to the two co-pilots who did not respond appropriately when the plane was in distress. Perhaps the most notable example was the Chernobyl nuclear reactor accident in the Ukraine in April, 1986. The reactor began to overheat at about 1:30am because critical cooling valves were shut off. The shiftworkers, sleep-deprived and likely experiencing microsleeps with consequent reduced decision-making ability, mistakenly disabled the cooling system, causing the reactor to overheat. As a result, there was a destructive explosion, resulting in numerous radiation-related injuries and casualties.

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Wikipedia