A microsleep is a sudden temporary episode of sleep or drowsiness which may last for a few seconds where an individual fails to respond to some arbitrary sensory input and becomes unconscious. Episodes of microsleep occur when an individual loses and regains awareness after a brief lapse in consciousness, often without warning, or when there are sudden shifts between states of wakefulness and sleep. In behavioural terms, microsleeps may 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.
Definition 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 microsleeps in a variety of contexts there is little agreement on how best to identify and classify microsleep episodes.
Causes Microsleeps frequently occur as a result of sleep deprivation. However, individuals who are not sleep-deprived or tired can also experience microsleeps during monotonous tasks.
Effects Microsleep is extremely dangerous when it occurs 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.
Background and significance
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, they are driving a car, and then suddenly realize that several seconds have passed by unnoticed. It is not obvious to the driver that they were 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 rail accident 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. A possible microsleep was recorded as part of the narrative verdict in the inquest into the 2016 Croydon tram derailment. Thus, microsleeps are often examined in the context of driver drowsiness detection and prevention of work-related injuries and public safety incidents (e.g. truck crashes, locomotive crashes, airplane crashes, etc.). Some statistics are below:
44% of drivers during late-night driving become dangerously sleepy. Extremely fatiguing work protocols increase accident probability from near 0% to 35%. Chronic microsleeps not only increase probability for injury but also decrease worker productivity and increase likelihood for absenteeism from work. According to one Centers for Disease Control and Prevention (CDC) study, among 74,571 adult respondents in 12 U.S. states, 35.3% reported <7 hours of sleep during a typical 24-hour period, 48.0% reported snoring, 37.9% reported unintentionally falling asleep during the day at least once in the preceding month, and 4.7% reported nodding off or falling asleep while driving at least once in the preceding month. The National Highway Traffic Safety Administration estimates that 2.5% of fatal crashes and 2% of injury crashes involve drowsy driving. Fatigue is associated with 250 fatalities in air carrier accidents in the last 16 years. Microsleep episodes are not dangerous in and of themselves. The risk comes from the potential that they carry to cause incidents resulting from lack of awareness. If an individual has occurrences of microsleep in an environment that is free from potential environmental risk and its associated consequences, then episodes of microsleep should be non-problematic.
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