Because one of the symptoms of fatigue is the decreased ability to judge your own level of tiredness, a typical response is to fight fatigue and try to stay awake. When a fatigued person is trying to stay awake in order to perform a monotonous task such as driving, microsleeps are likely to occur.

A microsleep is a brief, unintentional episode of loss of attention associated with events such as a blank stare, head snapping and prolonged eye closure. A microsleep is also known as “nodding off”. Microsleeps are unintended periods of light sleep that typically last between 2 and 30 seconds.

A person may not be 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.  If this occurs while driving, you may not see a red traffic signal, notice that the road has taken a curve or the traffic lanes are narrowing.