Why Do We Twitch When Falling Asleep? The Science of Hypnic Jerks

Oct 17, 2026 · 4 min read · Sourced and fact-checked

The short answer: A sudden jolt just as you drift off is called a hypnic jerk or sleep start. An Indian Journal of Psychiatry review says up to 70 percent of adults experience them, and that they are a normal part of the switch from wakefulness to sleep.

You are drifting off when your body suddenly jolts, sometimes with a vivid feeling of falling. That twitch has a name: a hypnic jerk, also called a sleep start. A 2025 article in the Indian Journal of Psychiatry explains what is known about them.

What a hypnic jerk is

Hypnic jerks are sudden, involuntary muscle contractions that happen during the transition from wakefulness to sleep. The movements are brief and non-stereotyped, meaning they do not follow a fixed pattern. They can be a bend or a straightening, often involve the neck and limb muscles, and are frequently accompanied by a racing heart or irregular breathing. They are also known as hypnagogic jerks or predormital myoclonus.

Very common and normally harmless

The article describes sleep starts as normal physiological events, experienced by up to 70 percent of the adult population at some point in life. They are benign and are not seizures. Unlike myoclonic seizures, hypnic jerks happen only at sleep onset, come with a normal EEG, and involve no tongue bite, loss of bladder control or confusion afterwards.

The falling feeling

Sleep starts are linked to at least one of three sensory experiences: a subjective feeling of falling, a sensory flash, or a brief dream-like image from the edge of sleep. That falling sensation is why so many people wake with a gasp and a grab at the bed.

What triggers them

The article lists fatigue, stress and sleep deprivation as triggers, and says the American Academy of Sleep Medicine also names anxiety, stimulants such as caffeine and nicotine, and strenuous activity in the evening. Certain medicines, including some stimulants and some antidepressants, can also bring them on.

Why the body does it

No single cause is established, but the article describes two main theories. One says the jerks are a natural part of the transition from alertness to sleep, handled by the reticular activating system, the brain network that manages wakefulness; as control shifts, nerves can misfire and produce a sudden movement. The other proposes a basic protective reflex: as the muscles relax completely, the brain may read that relaxation as a sign of falling, and fires a signal to the muscles to catch the body.

A note

A twitch at sleep onset is normal. If jerks happen repeatedly through the night, disturb sleep badly, or come with other symptoms, it is worth seeing a doctor. This is general information, not medical advice.

Sources

Escitalopram-induced hypnic jerks: An overlooked side effect (background and review of sleep starts), Indian Journal of Psychiatry, February 2025: https://pmc.ncbi.nlm.nih.gov/articles/PMC11964172/

Facts checked: October 17, 2026.