What Is a Hypnagogic Jerk and What Causes Sleep Starts?

Frequent Sudden Movements in Sleep May Require Further Evaluation

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Just after falling asleep, you may wake with a sudden jerking movement. What causes these so-called sleep starts? Learn about hypnagogic jerks, the most common symptoms, and whether further evaluation and treatment may be necessary.

What Is a Hypnagogic Jerk?

A hypnagogic jerk is a sudden and strong involuntary myoclonic twitch, or muscle contraction, that occurs while an individual is beginning to fall asleep.

The same phenomenon is called a hypnic jerk if it occurs upon awakening and both are often known as a sleep start. It may affect only part of the body, like an arm or leg, but it may more commonly seem to cause the entire body to jolt suddenly. In some cases, a vocalization or sharp cry may occur.

These movements may occur without waking the affected person. If an awakening does occur, these sudden movements are often associated with a brief mental image. For example, you might believe that you were falling. A leg movement may incite a dream image that you were perhaps kicking a soccer ball. It is believed that the movements occur first, perhaps due to an electrical discharge along the body's nerves, and that the mental image or explanation follows.

Why Do Sleep Starts Occur?

Sleep starts can be a normal part of sleep. It is estimated that 60-70% of people recall experiencing them. If they occur infrequently, they are not usually distressing.

However, frequent events may lead to anxiety about falling asleep and insomnia, especially if the recalled explanation for the movement is upsetting (such as falling from a great height).

Hypnagogic jerks typically occur during stage 1 sleep. This is the lightest stage of sleep that occurs immediately after falling asleep.

It may occur periodically later in the night.

Sleep starts occur more often with increased use of caffeine and other stimulants. It may be provoked by physical exercise or emotional stress. Frequent episodes may prompt further evaluation.

Further Evaluation and Treatment of Sleep Starts

In general, it is not necessary to seek further testing or treatment for sleep starts. Reassurance that this is a normal phenomenon is often all that is needed. If frequent movements occur - especially if they are associated with other complaints such as physical injury, mouth or tongue biting, bedwetting, or confusion upon awakening - it may be helpful to visit with a doctor to rule out other conditions.

Sometimes these awakenings can be provoked by another sleep disorder, most commonly disrupted breathing like sleep apnea. Sleep starts may be exacerbated by medication or substance use. In addition, movements in sleep can sometimes suggest seizures. It may be necessary to have a diagnostic sleep study called a polysomnogram.

Alternatively, an EEG may be ordered if seizures are suspected to be causing the uncontrolled movements.

If you have frequent sleep starts that are disturbing your sleep, or the sleep of your bed partner, you may want to speak with a sleep specialist to get the evaluation and treatment that you need.


Kryger, MH et al. "Principles and Practice of Sleep Medicine." Elsevier, 5th edition, 2011.

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