Hypnic jerk

A hypnic jerk, hypnagogic jerk, sleep start, sleep twitch, myoclonic jerk, or night start is a brief and sudden involuntary contraction of the muscles of the body which occurs when a person is beginning to fall asleep, often causing the person 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, sometimes accompanied by a falling sensation.<ref name="bbasics">Template:Cite web</ref> Hypnic jerks are associated with a rapid heartbeat, quickened breathing, sweat, and sometimes "a peculiar sensory feeling of 'shock' or 'falling into the voidTemplate:'".<ref name="Friedman2014">Template:Cite web</ref> It can also be accompanied by a vivid dream experience or hallucination.<ref name="Oswald">Template:Cite journal</ref> A higher occurrence is reported in people with irregular sleep schedules.<ref name="SSyllabus">Template:Cite web</ref> When they are particularly frequent and severe, hypnic jerks have been reported as a cause of sleep-onset insomnia.<ref name="Oswald" />

Hypnic jerks are common physiological phenomena.<ref name="Sander">Template:Cite journal</ref> Around 70% of people experience them at least once in their lives with 10% experiencing them daily.<ref name="Chokroverty">Template:Cite journal</ref><ref name="Vetrugno">Template:Cite journal</ref> They are benign and do not cause any neurological sequelae.<ref name="Vetrugno" />

Causes

According to the American Academy of Sleep Medicine (AASM), there is a wide range of potential causes, including anxiety, stimulants like caffeine and nicotine, stress, and strenuous activities in the evening. It also may be facilitated by fatigue or sleep deprivation.<ref name="Vetrugno" /> However, most hypnic jerks occur essentially at random in healthy people.<ref>Template:Cite journal</ref> Nevertheless, these repeated, intensifying twitches can cause anxiety in some individuals and a disruption to their sleep onset.<ref name="Chokroverty" />

Sometimes, hypnic jerks are mistaken for another form of movement during sleep. For example, hypnic jerks can be confused with restless leg syndrome, periodic limb movement disorder, hypnagogic foot tremor, rhythmic movement disorder, and hereditary or essential startle syndrome. But some phenomena can help to distinguish hypnic jerk from these other conditions. For example, the occurrence of hypnic jerk arises only at sleep onset and it happens without any rhythmicity or periodicity of the movements and EMG bursts. Other pertinent history can also be used to differentiate it.<ref name="Chokroverty" />

This physiological phenomenon can also be mistaken for myoclonic seizure, but it can also be distinguished by different criteria such as the fact that hypnic jerk occurs at sleep onset only or that the EEG is normal and constant. In addition, unlike seizures, there are no tongue bites, urinary incontinence, or postictal confusion in hypnic jerk. This phenomenon can therefore be distinguished from other more serious conditions.<ref name="Chokroverty" />

The causes of hypnic jerk is unclear and being studied. None of the several theories that have attempted to explain it have been fully accepted.<ref>Template:Cite web</ref> 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.<ref>Template:Cite web</ref> Another theory postulates that the body mistakes the sense of relaxation that is felt when falling asleep as a sign that the body is physically falling. As a consequence, it causes a jerk motion to wake the sleeper up so they can catch themselves.<ref name="Complete Guide to Hypnic Jerks">Template:Cite web</ref> 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.<ref name=Friedman2014 />

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.<ref name="Fisch2009">Template:Cite book</ref>

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".<ref name="Askenasy">Template:Cite journal</ref> 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.<ref name="Askenasy" />

Treatment

There are ways to reduce hypnic jerks, including reducing consumption of stimulants such as nicotine or caffeine, avoiding physical exertion prior to sleep, and consuming sufficient magnesium.<ref name="Sathe">Template:Cite journal</ref><ref name="Shady">Template:Cite journal</ref>

Some medication can also help to reduce or eliminate the hypnic jerks. For example, low-dose clonazepam at bedtime may make the twitches disappear over time.<ref name="Chokroverty" />

In addition, some people may develop a fixation on these hypnic jerks, leading to increased anxiety about the disruptive experience. This increased anxiety and fatigue increases the likelihood of experiencing these jerks, resulting in a positive feedback loop.<ref name="Hypnic Jerks: How To Avoid Waking With A Jolt">Template:Cite web</ref>

See also

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