Many people experience hypnic jerks, sudden muscle twitches, as they drift off to sleep. Some also experience sleep paralysis in that transitional period between wakefulness and sleep. Much research on sleep clarifies the causes, frequency, and differences between these phenomena. Dr. Amir Khan, NHS GP and health communicator, recently addressed these in his social media posts.
Hypnic jerks (also called hypnagogic jerks, sleep starts, or sleep myoclonus) occur as a person transitions from wakefulness into sleep, often during light sleep or just as they begin to fall asleep. These jerks are brief, involuntary muscle contractions. They can involve limbs, a startle sensation, or even feeling like one is falling. Research indicates that a majority of people have at least one hypnic jerk in their lifetime. The frequency and intensity vary. Some people have them occasionally; for others, they may be more frequent under certain conditions. 1,2
Causes linked to hypnic jerks include sleep deprivation, increased stress or anxiety, stimulants like caffeine, irregular sleep schedule, and being overly tired. These factors appear to increase the chance of experiencing hypnic jerks.
Sleep paralysis is a different but related phenomenon. Harvard Health describes it as a temporary inability to move or speak while one is conscious, and occurs during the transitions between sleep and wakefulness. Usually it happens either when falling asleep or when waking up. During such an episode, individuals are aware but cannot move limbs, speak, or sometimes even open their eyes. Often, vivid or frightening hallucinations accompany the event. 4
Sleep paralysis episodes usually last from a few seconds to a few minutes. They may include sensations of pressure on the chest, being choking, or seeing a presence in the room. Sometimes sleep paralysis occurs recurrently; in other cases it happens only once. Harvard notes two types: isolated sleep paralysis (without other sleep disorders) and recurrent isolated sleep paralysis (often without narcolepsy). 4
Dr. Amir Khan recently posted on X (formerly Twitter) about hypnic jerks, noting they are common and usually harmless. He also mentioned that some research says hypnic jerks might have been an ancient response of brain when humans use to sleep on trees. He emphasized that awareness of one’s sleep habits, stress, and environment can help reduce both hypnic jerks and sleep paralysis episodes.
| Phenomenon | When It Occurs | Main Features | Overlap / Relationship |
|---|---|---|---|
| Hypnic Jerks | Just as you fall asleep (light sleep onset) | Sudden muscle twitch, startle, possibly a feeling of falling; no conscious paralysis; typically brief | May occur in same transition to sleep where sleep paralysis can occur; both relate to sleep onset processes and may share triggers like stress or fatigue |
| Sleep Paralysis | Asleep‑wake boundary: falling asleep or waking up | Conscious awareness, inability to move/speak, sometimes hallucinations; muscle atonia persists temporarily; lasts seconds to minutes | Can share triggers with hypnic jerks; frequent hypnic jerks or poor sleep hygiene may increase risk of sleep paralysis episodes |
A 2022 study “Characteristics of Sleep Paralysis and Its Association with Psychological and Lifestyle Factors” (P. Wróbel-Knybel et al.) found that psychological stress, anxiety symptoms, irregular sleep schedules, and lifestyle factors correlate with more frequent sleep paralysis. 3
According to Harvard Health, sleep paralysis is linked with sleep deprivation, irregular sleep schedules, certain disorders (like narcolepsy), use of some medications, alcohol, and substance use. Sleeping position (on one’s back) also may increase risk. 4
Studies suggest episodes are often more frightening than dangerous, though repeated sleep paralysis can contribute to anxiety or interfere with sleep quality. Researchers emphasize these are REM-sleep related phenomena: muscle atonia (normal during REM) fails to turn off when awakening or just starting sleep.
Both hypnic jerks and sleep paralysis share some preventive strategies. Research and expert sources suggest:
Maintain regular, sufficient sleep: aim for consistent sleep and wake times. Avoid large fluctuations in sleep schedule.
Reduce stress and anxiety. Practices such as relaxation, mindfulness, avoiding stressful activities close to bedtime help.
Avoid stimulants (caffeine, nicotine) and alcohol close to bedtime.
Sleep environment matters: cool, dark, quiet, with comfortable mattress and pillows. Sleeping position: avoiding supine (on back) may help reduce sleep paralysis.
When hypnic jerks or sleep paralysis episodes happen, some people benefit from focusing on moving small parts of their body (e.g. fingers or toes) or blinking rapidly to break the episode.
Harvard Health also suggests if sleep paralysis is recurrent or accompanied by other symptoms (excessive daytime sleepiness, signs of narcolepsy), a medical evaluation, possibly including a sleep study (polysomnography), may be necessary.
Seek help if:
Episodes of sleep paralysis occur often, disturb sleep regularly, or lead to insomnia or anxiety.
There are other symptoms possibly indicating underlying sleep disorders (narcolepsy, REM-sleep disorder).
The hypnic jerks are very frequent, intense, or coincide with neurological symptoms.
Hypnic jerks and sleep paralysis occur in the transition zones between wakefulness and sleep. While hypnic jerks are generally brief muscle twitches, sleep paralysis involves temporary loss of voluntary movement with consciousness and sometimes hallucinations. Though both are common and usually not harmful, lifestyle, sleep hygiene, stress, and consistent sleep schedules can reduce their frequency. Medical evaluation can help when episodes become frequent or distressing.
References
SleepFoundation. “Hypnic Jerk: Why You Twitch When You Sleep.” July 25, 2025. https://www.sleepfoundation.org/parasomnias/hypnic-jerks
Chiaro, Giacomo, Giovanna Calandra-Buonaura, et al. “Hypnic jerks are an underestimated sleep motor phenomenon in patients with parkinsonism.” Sleep Medicine, 2016. https://pubmed.ncbi.nlm.nih.gov/28007358/
Alghamdi, S.A., “Hypnic Jerks, Major Depressive Disorder, and ...” 2023 PMC article. https://pmc.ncbi.nlm.nih.gov/articles/PMC10590197/
Restivo, Jenette. 2023. "Sleep Paralysis: Causes, Symptoms, and Treatments." Harvard Health Publishing, October 20. https://www.health.harvard.edu/diseases-and-conditions/sleep-paralysis-causes-symptoms-and-treatments.
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