Written by: Lana Adler
Medically Reviewed by: Dr. Sherrie Neustein
Updated November 20, 2020
Have you ever found yourself just about to drift off to sleep when suddenly you’re startled by a random jerk? That’s a hypnic jerk. Hypnic jerks go by many names, including sleep starts, myoclonic jerks, sleep twitches, and hypnagogic jerks. The word hypnagogic describes the transitional stage between wakefulness and sleep. Hypnic jerks are so-called because that’s precisely when they occur.
What is a Hypnic Jerk?
Hypnic jerks are short, involuntary muscle jerks or twitches that occur right as you are falling asleep. Their involuntary nature makes them a myoclonus, a category of muscles that also includes hiccups. Myoclonic jerks are involuntary muscle twitches that occur quickly, with the muscles immediately returning to relaxation. Hypnic jerks happen randomly, but they always take place while someone is transitioning from wakefulness to sleep.
Hypnic jerks are distinct from the movements associated with sleep disorders like periodic limb movement disorder (PLMD) and restless leg syndrome (RLS). Hypnic jerks occur during the transitionary period between wakefulness and sleep, while RLS symptoms occur before sleep and PLMD movements occur during sleep. Both PLMD and RLS symptoms last longer than hypnic jerks, and typically only only involve the lower legs and feet, while hypnic jerks can affect one side of the body.
What Do Hypnic Jerks Feel Like?
Hypnic jerks can vary in intensity. They could be strong enough to rouse you back to alertness, or they could be so mild that you don’t even notice them. In fact, it’s common to sleep through your hypnic jerks. Some people are only aware they experienced them because their sleep partner told them.
Typically, hypnic jerks only affect one part or side of your body. It’s most common to experience a single hypnic jerk, although several could occur in succession. Often, people experience accompanying sensations with a hypnic jerk. These may include:
- A feeling of falling
- A banging, snapping, or crackling sound
- Visual symptoms like flashing lights, or a dream or hallucination
While less common, people may also report a sensation of pain or tingling.
How Frequently Do Hypnic Jerks Happen?
Around 60 to 70 percent of individuals experience hypnic jerks. Hypnic jerks affect both sexes, and for most people, they occur randomly and sporadically. You can also experience hypnic jerks at any age.
What Causes Hypnic Jerks?
There’s no official consensus on what causes hypnic jerks. Scientists have identified that myoclonus originates in the brain, either in the cerebral cortex or in the part of the brainstem responsible for your startle response. As for what specifically causes a hypnic jerk to occur, however, scientists remain undecided. It’s possible that during the transition from wakefulness to sleep, the neurotransmitters in these areas become unstable and cause hypnic jerks.
Regardless of their specific cause, scientists have determined certain factors may increase the frequency of hypnic jerks. These factors include anxiety, sleep deprivation, late-night exercise, and excessive use of caffeine and stimulants.
Emotional Stress and Anxiety
Anyone who’s been under stress knows how hard it can make it to sleep. That’s because anxious or stressful thoughts activate your brain. Even as your body tries to relax into sleep, these thoughts can wake up your brain, potentially causing movements like hypnic jerks to occur.
If you experience intense or frequent hypnic jerks, it’s possible you could develop anxiety around sleep itself. This can lead to insomnia and resulting sleep deprivation. Sleep deprivation, and poor sleep in general, may be another cause of hypnic jerks.
Like anxiety, exercise activates the body, waking you up and energizing you to take action. While this is great for getting you energized during the day, at night it can make it hard for your body to slow down for sleep. Intense physical activity or exercise late in the evening may lead to hypnic jerks.
Caffeine and Stimulant Use
Caffeine, nicotine, and other stimulants also wake up the brain and body. Excessive use of these, especially in the later afternoon and evening, can contribute to sleep-onset insomnia and less restful sleep overall. Lingering chemicals from these substances may interrupt your sleep and cause a hypnic jerk to occur.
Potential Evolutionary Origins
Recent research suggests a potential evolutionary origin for hypnic jerks. The theory goes like this: as primates were falling asleep, typically in trees, their brain interpreted that transition to relaxation as a threat to their survival. If they relaxed, they might fall out of the tree and injure themselves. Researchers hypothesize that hypnic jerks helped the primates adjust their sleeping positions to a safer position that would prevent them from falling or getting injured.
Are Hypnic Jerks Dangerous?
Hypnic jerks are not dangerous. They are a normal and common experience of falling asleep.
At worst, hypnic jerks can be a mild irritation. There’s also a chance that you could accidentally injure yourself or your sleep partner, but it shouldn’t be anything serious. The biggest risk hypnic jerks pose is any anxiety that arises from experiencing them, and wanting to avoid or put off sleep as a result. If this becomes a habit, it can lead to insomnia and sleep deprivation. Speak to your physician if you are experiencing these or any other sleep difficulties.
Can You Prevent Hypnic Jerks?
Hypnic jerks can be prevented, or occur less often, with a few simple lifestyle changes. Consider these tips to improve your sleep and reduce hypnic jerks.
Lower Your Stress and Anxiety.
Everyday stress and worries can be relieved with relaxation techniques, such as meditation or deep breathing exercises. A bedtime routine can also help calm the body before bed. Follow a simple set of relaxing activities each night, such as taking a warm bath, listening to music, or reading a book. Individuals living with chronic stress or anxiety should seek help from a mental health professional and their primary care physician.
Improve Your Sleep Hygiene.
Better sleep habits can help you get more sleep, and stave off the insomnia and sleep deprivation that may worsen hypnic jerks. Follow a regular sleep schedule every day, and ensure you are leaving enough room for at least 7 hours of sleep. Make your bedroom more hospitable to sleep and relaxation by cooling the temperature, turning down the lights, and removing electronics and clutter from the room.
Avoid Caffeine and Drugs.
Caffeine is fine to consume during the day in healthy amounts. However, consumption into the late afternoon and evening can interfere with your ability to fall asleep. Watch out for surprise sources of caffeine besides coffee, like chocolate. Drugs and alcohol can also interfere with sleep quality.
Exercise Earlier in the Day.
Regular exercise can improve sleep — so long as it is done earlier in the day. Avoid exercising at night so your body can relax better before bedtime, preventing hypnic jerks. If you love exercising at night, limit yourself to less intense activities like gentle yoga and stretching.
Remember, these tips may only reduce the occurrence of hypnic jerks. It’s normal to experience them from time to time, as they are a common and generally harmless part of the sleep experience.
The International Classification of Sleep Disorders – Third Edition (ICSD-3). Accessed October 2020.
https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Fact-Sheets/Myoclonus-Fact-Sheet. Accessed October 2020.
https://pubmed.ncbi.nlm.nih.gov/22033804/. Accessed October 2020.
https://doi.org/10.5664/jcsm.3170. Accessed October 2020.
https://pdfs.semanticscholar.org/0671/ea54bfee5a4c60ead7592f73dd4893a268ef.pdf. Accessed October 2020.