Drivers can experience microsleeps up to a thousand times per day.

Microsleeps are brief, unintended episodes of loss of attention associated with events such as blank stare, head snapping, and prolonged eye closure which may occur when a person is fatigued but trying to stay awake to perform a monotonous task like driving a car or watching a computer screen.

Microsleep episodes last from a few seconds to several minutes, and often the person is not aware that a microsleep has occurred. In fact, microsleeps often occur when a person's eyes are open. While in a microsleep, a person fails to respond to outside information. A person will not see a red signal light or notice that the road has taken a curve, which is why this phenomenon is of particular interest to people who study drowsy driving.

Microsleeps are most likely to occur at certain times of the day, such as pre-dawn hours and mid-afternoon hours when the body is "programmed" to sleep. Microsleeps increase with cumulative sleep debt. In other words, the more sleep deprived a person is, the greater the chance a microsleep episode will occur.

People with sleep disorders often experience microsleeps . It should be noted that “Excessive Daytime Sleepiness”, a well recognized symptom, is not the same as microsleep, although microsleep episodes often occur during periods of Excessive Daytime Sleepiness.