Definition: A hypnagogic jerk is an involuntary myoclonic twitch, or muscle contraction, that occurs while an individual is beginning to fall asleep. There may be a sensation of falling followed by a physical jerk back into wakefulness. It usually occurs during stage 1 sleep which is the lightest stage of sleep.
Also Known As: Hypnic jerk, Sleep starts
Examples:When I fall asleep, I startle myself back awake with a hypnagogic jerk.