Hypnic jerk

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Hypnic jerk
Classification and external resources
SpecialtySleep medicine

A hypnic jerk, hypnagogic jerk, sleep start, sleep twitch, myoclonic jerk, or night start is an involuntary twitch which occurs when a person is beginning to fall asleep, often causing them to jump and awaken suddenly for a moment. Hypnic jerks are one form of involuntary muscle twitches called myoclonus. Physically, hypnic jerks resemble the "jump" experienced by a person when startled,[1] sometimes accompanied by a falling sensation.[2] Hypnic jerks are associated with a rapid heartbeat, quickened breathing, sweat, and sometimes "a peculiar sensory feeling of 'shock' or 'falling into the void'".[3] A higher occurrence is reported in people with irregular sleep schedules.[4]


According to the American Academy of Sleep Medicine there is a wide range of potential causes, including anxiety, caffeine, stress and strenuous activities in the evening. However, most hypnic jerks occur essentially at random in healthy people.[5]

One hypothesis posits that the hypnic jerk is a form of reflex, initiated in response to normal bodily events during the lead-up to the first stages of sleep, including a decrease in blood pressure and the relaxation of muscle tissue.[6] A researcher at the University of Colorado suggested that a hypnic jerk could be "an archaic reflex to the brain's misinterpretation of muscle relaxation with the onset of sleep as a signal that a sleeping primate is falling out of a tree. The reflex may also have had selective value by having the sleeper readjust or review his or her sleeping position in a nest or on a branch in order to assure that a fall did not occur", but evidence is lacking.[7]

During an epilepsy and intensive care study, the lack of a preceding spike discharge measured on an epilepsy monitoring unit, along with the presence only at sleep onset, helped differentiate hypnic jerks from epileptic myoclonus.[8]

According to a study on sleep disturbances in the Journal of Neural Transmission, a hypnic jerk occurs during the non-rapid eye movement sleep cycle and is an "abrupt muscle action flexing movement, generalized or partial and asymmetric, which may cause arousal, with an illusion of falling".[9] Hypnic jerks are more frequent in childhood with 4 to 7 per hour in the age range from 8 to 12 years old, and they decrease toward 1 or 2 per hour by 65 to 80 years old.[9]

See also[edit]


  1. ^ Medical College of Wisconsin, Sleep: A Dynamic Activity
  2. ^ National Institute of Neurological Disorders and Stroke, Brain Basics: Understanding Sleep
  3. ^ Why You Sometimes Feel Like You're Falling And Jerk Awake When Trying To Fall Asleep by Lauren F Friedman, Business Insider, May 21, 2014
  4. ^ "Basics of Sleep Behavior: NREM and REM Sleep".
  5. ^ A Case of the Jerks by Kaitlyn Syring, University Daily Kansan, February 28, 2008
  6. ^ Castro, Joseph. "Why Do People 'Twitch' When Falling Asleep?". LiveScience.
  7. ^ "Why You Sometimes Feel Like You're Falling And Jerk Awake When Trying To Fall Asleep". Retrieved 2016-07-17.
  8. ^ Fisch, Bruce J. Epilepsy and Intensive Care Monitoring: Principles and Practice. New York: Demos Medical, 2010.
  9. ^ a b Askenasy, J. J. M. (2003). "Sleep Disturbances in Parkinsonism" (PDF). Journal of Neural Transmission. Springer-Verlag. 110: 125–50. doi:10.1007/s007020300001.

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