Definition: A hypnic jerk is an involuntary muscle contraction, sometimes called a myoclonic twitch, that occurs during the lightest stage of sleep. This stage 1 sleep occurs as you begin to fall asleep. There may be a sensation of falling followed by a physical jerk back to wakefulness.
Also Known As: Hypnagogic jerk, Sleep starts
Examples: When I fall asleep, I startle myself back awake with a hypnic jerk.
