APA Dictionary of Psychology

n. a momentary loss of awareness when a person is fatigued or sleep-deprived, especially during monotonous tasks, such as driving, looking at a computer, or passively monitoring machinery. Microsleep episodes may be noticed when the head literally drops forward and can last from less than 1 second to minutes. They are more likely to occur in the predawn and midafternoon hours and can be a major risk factor for traffic and industrial accidents.