Experiencing sudden muscle jerks before falling asleep is a common yet puzzling phenomenon that scientists have yet to fully understand.

As sleep approaches, a sudden sensation akin to free-falling or an unexpected jolt may occur, leaving limbs or the entire body twitching involuntarily.

This fleeting "fight or flight" response can abruptly disrupt the calm of bedtime. For many, this phenomenon—known as "hypnic jerks" or "sleep starts"—can feel unsettling or strange. In fact, around 70% of people experience it at least once in their lifetime, with about 10% encountering it regularly. Despite its prevalence, the scientific community remains uncertain about its underlying causes.

A 2018 study published in Current Sleep Medicine Reports summarized hypnic jerks as an intriguing sleep phenomenon requiring further research to clarify its physiological mechanisms and origins. Years later, this conclusion still holds.

Hypnic Jerks: Falling Sensation When Going to Sleep

Video by Hashem Al-Ghaili

What Do We Know About Hypnic Jerks?

Dr. Allen Richert, a professor of psychiatry and sleep medicine at the University of Mississippi Medical Center, states that no definitive explanation exists for hypnic jerks. These jerks involve coordinated muscle movements triggered by signals from the central nervous system, but the exact cause of these signals remains unknown.

Although their origin is unclear, experts classify hypnic jerks as a type of myoclonic spasm—sudden, involuntary muscle contractions similar to hiccups or even seizures. However, unlike seizures, hypnic jerks are benign and not indicative of any underlying health issues.

The American Academy of Sleep Medicine (AASM) has identified potential triggers, including excessive caffeine consumption, high stress levels, intense physical activity, or sleep deprivation. In essence, both heightened excitement and extreme fatigue may increase the likelihood of hypnic jerks.

Dr. Richert elaborates that while sleep deprivation might elicit certain physiological responses, there’s no evidence suggesting that sleeping more can prevent these jerks or that insufficient sleep exacerbates them.

Theories About Hypnic Jerks

Various hypotheses have been proposed to explain this phenomenon:

Misperception by the Brain: As blood pressure drops and muscles relax, the brain may mistakenly interpret this state as a potential threat, briefly triggering a panic-like response.

Evolutionary Roots: Another theory posits that hypnic jerks are a protective mechanism rooted in the instincts of our primate ancestors. This reflex may have evolved to prevent falls from trees during sleep by quickly jolting the body awake.

Managing Hypnic Jerks

Currently, no medications or behavioral adjustments have been proven to reliably reduce hypnic jerks. The AASM recommends adopting good sleep hygiene practices, including:

Avoiding caffeine and other stimulants before bed.

Reducing stress through relaxation techniques.

Ensuring consistent and sufficient sleep.

If hypnic jerks or related concerns do not significantly impact daily life, seeking medical attention is generally unnecessary. Dr. Richert and other experts agree that hypnic jerks are a fascinating, albeit enigmatic, part of human evolution. While their exact purpose remains a mystery, they are harmless and not worth losing sleep over.