When you are falling asleep, you may feel hypnic jerks, also known as

sleep beginnings, which are abrupt, involuntary contractions of your muscles.

These jerks happen during the transition from wakefulness to sleep,

which is referred to as hypnagogic (short for hypnic).

Hypnic jerks usually only affect one side of the body, like the left

arm or leg, and occur seemingly randomly as you fall asleep.

Why Does My Body Twitch at Random Times at Night?

Although the exact cause of hypnic jerks is unknown, there are some ideas.

The same area of the brain that regulates your startle response is where hypnic

jerks and other forms of myoclonus begin. It is thought that a misfire between

nerves in the reticular brainstem occasionally happens while you fall asleep, causing a reflex that results in a hypnic jerk.

For instance, your brain can erroneously believe that you are actually falling

when your muscles fully relax, even though this is a typical aspect of falling

asleep, and respond by causing your muscles to twitch. Another possibility is

that hypnic jerks are a bodily response to the accompanying dreamlike images.

A hypnic jerk may be more likely to occur if you have certain risk factors,

such as excessive caffeine and stimulant use, intense activity right before bed, emotional stress, and lack of sleep.

Excessive Caffeine or Nicotine Consumption

Caffeine and nicotine are examples of stimulants that awaken the brain. These drugs can also interfere with sleep by remaining

in your system for a number of hours. People in one study still had problems falling asleep even after quitting coffee six hours

before bed. Hypnic jerks can result from consuming excessive amounts of caffeine or nicotine or by doing so too soon before

bed.