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A hypnic jerk, hypnagogic jerk, sleep start, sleep twitch or night start, or jump, is an involuntary twitch which occurs just as a person is beginning to fall asleep, often causing them to awaken suddenly for a moment. Physically, hypnic jerks resemble the "jump" experienced by a person when startled,〔Medical College of Wisconsin, ''Sleep: A Dynamic Activity''〕 often accompanied by a falling sensation.〔National Institute of Neurological Disorders and Stroke, (Brain Basics: Understanding Sleep )〕 Hypnic jerks are associated with a rapid heartbeat, quickened breathing, sweat, and sometimes "a peculiar sensory feeling of 'shock' or 'falling into the void.'"〔(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〕 A higher occurrence is reported in people with irregular sleep schedules.〔(Basics of Sleep Behavior: NREM and REM Sleep )〕 ==Causes== 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 randomly in healthy people.〔 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.〔Fisch, Bruce J. ''Epilepsy and Intensive Care Monitoring: Principles and Practice''. New York: Demos Medical, 2010.〕 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." Hypnic jerks are more frequent in childhood with 4–7 per hour at the age ranging from 8 to 12 years old, and it decreases toward 1–2 per hour at 65 to 80 years old.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「hypnic jerk」の詳細全文を読む スポンサード リンク
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