Hypnic jerks, also known as hypnagogic jerks or “sleep starts,” are involuntary muscle contractions that some people experience as they fall asleep.

Hypnic jerks are a type of sleep myoclonus. This is a scientific name for jerking movements the body makes during sleep or while falling asleep.

Some hypnic jerks are mild and hardly noticeable. Others can be intense — anyone who has been close to falling asleep and then felt a sudden jerk that has woken them up has experienced them.

Hypnic jerks are common and occur randomly. And while the exact cause of these twitches is unclear, some factors may increase their likelihood.

Hypnic jerks are not dangerous. A person experiencing them does not need to consult a doctor or seek medical treatment unless they cause distress or other symptoms, such as incontinence, injury, pain, or confusion.

This article explores hypnic jerks, how common they are, and how to reduce their frequency.

A hypnic jerk is an involuntary twitch of one or more muscles that occurs as a person falls asleep. It tends to occur in stages 1 or 2 of sleep and disappear in stage 3, which refers to rapid eye movement sleep. In other words, they occur when a person transitions from a wakeful state to a sleeping state.

Hypnic jerks are a type of involuntary muscle movement called myoclonus. Hiccups are another common form of myoclonus.

The strength of a hypnic jerk may vary. Some people may not be aware of their body movements and only know that they have them if a partner or caregiver notices them. Other times, the spasms can be strong enough to startle the person and wake them up.

People may experience other symptoms alongside hypnic jerks, such as:

  • feeling as though they are falling or tripping
  • a sensory flash, which may feel like an electric shock
  • a hallucination or vivid dream, often about falling

These sensations are not signs of any underlying health conditions. However, if they are intense, they may prevent the person from falling asleep, leading to insomnia.

Sleep myoclonus is when people’s bodies twitch or jerk while sleeping or falling asleep. Learn more.

The authors of a 2016 study noted that hypnic jerks occur randomly and affect people of all ages.

Additionally, the researchers found that 60–70% of individuals experience hypnic jerks, usually just as they are about to fall asleep. However, people who experience them do not usually have them every time they sleep.

In most cases, there is no clear cause of a hypnic jerk. They occur in most people without any underlying explanation.

However, there are some ideas and theories about why these sleep starts occur.

Possible reasons may include the below.

Extreme tiredness and sleep deprivation

Overtiredness is a common cause of hypnic jerks. They can also occur when someone goes to sleep in an uncomfortable position.

Stimulants

Body and brain stimulants, such as caffeine, nicotine, or some drugs, may make falling asleep or staying asleep difficult. They may also increase the frequency of hypnic jerks.

Stress and anxiety

High levels of stress and anxiety can make it difficult to relax in preparation for sleep. An alert brain may be easier to startle, so a person may be more likely to wake up when these involuntary muscle twitches occur.

Results from research using an EEG suggest specific brain activity occurs during a hypnic jerk, known as vertex sharp waves.

Sleep starts can occur in people of all ages. The American Academy of Sleep Medicine notes that adults are more likely than children to complain about frequent or intense hypnic jerks.

However, children can experience hypnic jerks from birth. The author of one older study from 2003 describes myoclonus, or uncontrollable body movements, as a developmental feature of the human nervous system, present from the early stages of fetal development.

Hypnic jerks can cause a person to wake up, but this does not always occur. It depends on the intensity of the muscle contraction.

Smaller movements are unlikely to wake a person up. They may only be aware that they experience hypnic jerks if a partner or caregiver notices them.

The other symptoms of a hypnic jerk may also wake someone up. Sometimes, a person may dream that they are falling out of bed, from a tree, or through a void. Although it is uncertain which sensation comes first, this can be enough to scare people awake.

While it may not be possible to avoid all instances of hypnic jerks, some people may notice that they have them less frequently when they make a few lifestyle changes.

Tips that may help prevent hypnic jerks include:

Avoiding over-tiredness

A person can avoid excessive tiredness by getting sufficient quality sleep.

Tips for sleeping well include:

  • ensuring a room is dark, quiet, and of a suitable temperature
  • keeping electronic devices outside the room
  • going to bed and getting up at the same time each day, if possible
  • exercising during the day

Get some tips on managing sleep while on night shifts.

Avoiding caffeine

Caffeine sources, such as coffee, tea, and chocolate, may help a person wake up. However, having caffeine later in the day may overstimulate the body and brain, making it difficult to transition to sleep.

Avoiding other stimulant drugs

Other stimulating drugs, such as nicotine and alcohol, may affect sleep. Using them may result in sleep deprivation or disruptive hypnic jerks.

Seek help for stress and anxiety

Hypnic jerks may be more intense in people with anxiety. Addressing stress and anxiety may help reduce their intensity.

Learn about eight ways to calm anxious thoughts.

Creating a bedtime routine

A bedtime routine may help the body relax and reduce stress. Some people drink calming teas or warm milk and read a book before bed. Others may prefer to do gentle stretches or listen to music.

Discover some tips on getting better sleep.

Turning down the lights

Research shows that light stimulates the brain to be more alert, meaning that while it may help someone wake up more easily, it could make sleep more difficult.

Blue light — the cold light from some light bulbs, televisions, computer monitors, and smartphones tells the body that it is daytime.

Turning down these lights or avoiding digital screens before bed will reduce the levels of blue light and may help a person relax.

However, there is no evidence that it will prevent hypnic jerks.

Relaxing meditations

Some people use guided meditations or breathing exercises to help them relax. Taking slow, deep breaths for 5 minutes may help them reduce stress levels.

Try these sleep apps to help with sleep and relaxation.

Hypnic jerks, or sleep starts, are typical and common. Experiencing them does not mean that a person has an underlying medical condition.

Certain lifestyle changes may help people reduce the number of hypnic jerks they experience.

Anyone with concerns about frequent hypnic jerks and their overall health or sleep quality can speak with a doctor.

In some cases, healthcare professionals can prescribe medications to help them get more restful sleep.