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Hypnagogic vs. Hypnic Jerks
Why Sleep Starts Occur
Further Evaluation
Frequently Asked Questions
Just after falling asleep, you may wake with a sudden jerking movement. What causes these so-called sleep starts? Learn about hypnagogic jerks, or hypnic jerks, including the most common symptoms, and whether further evaluation and treatment may be necessary.
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Hypnagogic vs. Hypnic Jerks
Ahypnagogicjerk is a sudden and strong involuntary 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.
Both are often known as a sleep start. It may affect only part of the body, like an arm or leg. 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 fragmentary 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. In a sense, the brain creates a story to account for the movement.
Why Do Sleep Starts Occur?
Sleep starts can be a normal part of sleep. It is estimated that 60 to 70 percent of people recall experiencing them. If they occur infrequently, as they often do, they are not usually distressing.
However, frequent events may lead toanxietyabout falling asleep andinsomnia, especially if the recalled explanation for the movement is upsetting (such as falling from a great height).
Hypnagogic jerks typically occur duringstage 1 sleep. This is the lightest stage of sleep that occurs immediately after falling asleep. It may be misinterpreted as wakefulness, leading to confusion about when sleep starts to occur.
It may occur periodically later in the night, but these events are less likely to be recalled.
What Is a Sleep Study (Polysomnogram)?
Beyond sleep starts, there are other conditions that may contribute to movements during the transition to our state of sleep. If you experience frequent sleep movements, several other causes may be considered.
Restless Leg Syndrome
Natural Remedies for Restless Leg Syndrome
Occurring during sleep, periodic limb movements consist of flexion and extension of the foot (and sometimes knee) in a rhythmic fashion.
These occur periodically in trains of events but may come and go in the night. Unlike hypnagogic or hypnic jerks, these are not single, isolated events.
Seizures
Depending on the type of seizure, there may be a large movement of the body. Generalizedtonic-clonic seizuresmay be associated with tongue or mouth biting, loss of bladder control with incontinence, and even injuries.
After the episode, there may be a period of confusion. These last 1 minute on average and are usually easy to distinguish from sleep starts.
Seizures: Types in Children and Adults
Shivering
If the sleep environment is cold, ora feverexists, it is possible that shivering may cause movements in sleep. This high-frequency movement may affect the extremities with the whole body.
These typically last longer than sleep starts, which are often sudden events that immediately resolve, and resolve with warming the body or treating the fever.
Fasciculations
If a specific muscle or group of muscles twitch, this may be called a fasciculation. It appears like quivering and may even look like a “bag of worms.” These movements may occur across a joint and cause the contraction to move the extremity.
Fasciculation generally are more persistent than a sleep start and may be noted during wakefulness.
Benign Fasciculation Syndrome: Causes and Treatment
Further Evaluation 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.
In addition, movements in sleep can sometimes suggest seizures. It may be necessary to have a diagnostic sleep study called apolysomnogram.Alternatively, anEEGmay be ordered if seizures are suspected to be causing the uncontrolled movements.
A Word From Verywell
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 board-certified sleep physician to get the evaluation and treatment that you need.
It’s not possible to fully prevent hypnic jerks from occurring, but there are certain bedtime habits you can adopt to reduce their risk of waking you up. When you go to sleep, be sure to make your sleep environment as dark and quiet as possible. If noise is an issue, consider using bedtime earplugs or a white noise machine to drown out external sounds. Try sleeping at the same time each night, and avoid electronic devices at least half an hour before sleeping.
No, you cannot have hypnic jerks while wide awake. Hypnic jerks only happen while waking up from sleep or during sleep.Muscle twitcheswhile awake could be a fasciculation, or muscle twitching and quivering that can sometimes be powerful enough to move a joint.
What to Know About Sleep Myoclonus
3 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
American Academy of Sleep Medicine.Sleep Starts.
Sleep Foundation.Hypnic Jerks.
Berry RB, Brooks R, Gamaldo CE, et al.The AASM Manual for the Scoring of Sleep and Associated Events: Rules, Terminology and Technical Specifications, Version 2.2. American Academy of Sleep Medicine.Kryger, MH, et al.Principles and Practice of Sleep Medicine.Elsevier, 6th edition.
Berry RB, Brooks R, Gamaldo CE, et al.The AASM Manual for the Scoring of Sleep and Associated Events: Rules, Terminology and Technical Specifications, Version 2.2. American Academy of Sleep Medicine.
Kryger, MH, et al.Principles and Practice of Sleep Medicine.Elsevier, 6th edition.
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