Hypnic jerks, which people also refer to as hypnagogic jerks or “sleep starts,” are involuntary muscle contractions that some people experience as they are 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 a hypnic jerk.

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

In this article, learn more about hypnic jerks, how common they are, and how to reduce their frequency.

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Hypnic jerks occur when a person is transitioning to a sleeping state and may wake them up.

A hypnic jerk is an involuntary twitch of one or more muscles that occurs as a person is falling asleep. It tends to happen just as the person is transitioning 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 the twitches, and may only know that they experience them if a partner or caregiver notices the movements. 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
  • rapid heartbeat
  • rapid breathing
  • sweating
  • dreaming about falling

These sensations are not signs of any underlying health conditions.

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

The researchers found that 60 to 70 percent of people experience hypnic jerks, usually just as they are about to fall asleep.

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

With that said, there are some ideas and theories about why these sleep starts occur. Possible reasons may include:

Exercise: Exercising stimulates the body, so exercising late in the evening may make it more difficult for the body to relax in time for sleep. This excess stimulation may cause a hypnic jerk.

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

Stress and anxiety: A high-stress lifestyle or feeling very anxious 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.

Poor sleep habits: Irregular sleep patterns, sleep deprivation, or regular sleep disturbances may lead to hypnic jerks.

Sleep starts can happen in people of all ages. However, the American Academy of Sleep Medicine note that adults are more likely than children to complain about frequent or intense hypnic jerks.

The reason for this may be that many of the factors that sleep specialists associate with sleep starts are not generally relevant to children, such as:

  • caffeine intake
  • emotional stress
  • intense physical exercise

However, this does not mean that hypnic jerks are not possible in younger children or that they indicate a problem. They may simply be less common in people of this age.

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A hypnic jerk may be significant enough to shock a person awake.

It is possible to wake up from a hypnic jerk, but this does not always happen, as the strength of the muscle contraction that a person experiences will vary.

Some people only have minor hypnic jerks and are very unlikely to wake up because of them. They may only be aware that they experience hypnic jerks if a partner or caregiver notices them.

In other cases, a muscle contraction may be significant enough to shock the person awake. The strength of the contraction itself or the unsettling feeling that the person has from moving so quickly could cause this. In some cases, these large contractions can make a person feel as though someone else is pushing them off the bed.

The other symptoms of a hypnic jerk may also wake the person up. Sometimes the person dreams that they are falling either out of bed, from a tree, or through a void. Although it is uncertain which sensation comes first, this can be enough to scare the person 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 late-night exercise

Exercise is vital, but too much physical stimulation close to bedtime may increase the likelihood of these muscle twitches.

Exercising earlier in the day instead can give the body plenty of time to relax and unwind before bed.

Avoiding caffeine

Caffeine sources, such as coffee, tea, and chocolate, may help a person wake up in the morning, but having caffeine later in the day can stimulate the body and brain too much, making it difficult to transition to sleep.

Avoiding other stimulant drugs

Other stimulating drugs, such as nicotine and alcohol, may lead to restless sleep, which can result in issues with sleep deprivation or disruptive hypnic jerks.

Creating a bedtime routine

Creating 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.

Turning down the lights

Researchers know that light stimulates the brain to be more alert, which means that it can help a person wake up more easily in the morning but could make sleep more difficult.

Blue light, which is 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 technology before bed will reduce the levels of blue light and may help a person relax.

Relaxing meditations

Some people use guided meditations or breathing exercises to help them relax. Something as simple as taking slow, deep breaths for 5 minutes may help a person reduce their stress levels.

Hypnic jerks, or sleep starts, are normal 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 that they experience.

Anyone who is experiencing hypnic jerks regularly and is concerned about their overall health or sleep quality should talk to a doctor.

In some cases, doctors can prescribe medications to help a person get more restful sleep and avoid hypnic jerks.