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, MSs 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. MSs frequently occur as a result of sleep deprivation. However, healthy individuals who are not sleep-deprived or tired 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. 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 (i.e. the train's engineer) had a heart attack, and the guard (i.e. the train's conductor) 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