What is a hypnic jerk?

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.

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. 

 
Frequency

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.

Causes

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.

 
Hypnic jerks in children and babies

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.

Can hypnic jerks wake us up?

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