Hypnic jerks also called hypnagogic jerks, sleep jerks, sleep twitches, or sleep starts, are small, involuntary muscle movements that occur right before you fall into a deep sleep. If you have experienced this, or if you've ever watched someone suddenly wake up because of a foot twitch, you may want to find out why.
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You probably have slept through sleep starts, but if you happen to feel some twitching while you are asleep, it will most likely wake you up. You might feel like you're falling, and suddenly get alarmed and wake up. Although less common, you may also experience sensations of pain or tingling.
Hypnic jerks typically affect one side of your body, and it's common for some people to experience only a single jerk, although you may experience several in quick succession. No matter how many jerks you experience, make sure to take a deep breath, calm yourself, and try to go back to sleep.
Hypnic jerks fall under a wider umbrella of muscle movements called myoclonus¹ which is a sudden, short, and involuntary muscle movement. There are two types of myoclonus:
Negative myoclonus – when a muscle movement suddenly stops.
Positive myoclonus – when a muscle suddenly contracts.
Sleep starts occur under a category of sudden muscle movements called physiologic myoclonus, which is a brief muscle twitch followed by muscle relaxation. Sleep starts are similar to hiccups, and they occur in healthy people with no neurological disorders.
Apart from the obvious muscle twitches, you may also experience increased heartbeat, rapid breathing, sweating, clammy skin, and a falling sensation. These symptoms vary from person to person and are normal, so don’t be worried if you experience one or more of them.
The cause of hypnic jerks remains a mystery, as researchers do not know for certain what causes this phenomenon. Hypnic jerks happen just as you're falling asleep before your brain drifts off into REM sleep. It also happens as you shift from one sleeping state to another throughout the night.
One theory attempts to explain the reason behind hypnic jerks by suggesting that your brain doesn't interpret your body state accurately when you experience sleep starts. Since your body is in a light sleep state, your brain 'thinks' you're still awake but notices that none of your muscles are moving, so it sends some unusual signals to your muscles to initiate a movement – or it jolts you awake.
There are both chemical and physiological triggers² to hypnic jerks. One chemical trigger is caffeine in your bloodstream. While your body is trying to power down and sleep, the caffeine that is still circulating in your bloodstream will jolt your brain, which in turn sends movement signals to your muscles. Alcohol and stimulating drugs also have the same effect. Physiological factors include stress, exercise, and lack of sleep.
When you're stressed, your mind keeps racing even when you are trying to sleep. This causes your brain to try and startle your muscles to keep up with the brain's activity. Lack of sleep disrupts your normal sleep cycle, making it more likely that you will experience hypnic jerks.
Physical exercise also stimulates your body and can trigger hypnic jerks. If you sleep right after a rigorous exercise session, you'll are very likely to experience hypnic jerks as you fall asleep, since your body is stimulated but you have suddenly stopped muscle movement. This is what medical experts call negative myoclonus.
Hypnic jerks are a fairly common natural phenomenon and are completely natural. Up to 70%³ of people have experienced sleep starts at some point in their lives.
It's important to realize that hypnic jerks are not a neurological disorder. Sleep starts are rarely a sign of any underlying condition. If you're experiencing hypnic jerks several times a day, you may want to reduce your caffeine intake,⁴ avoid alcoholic beverages, stimulating drugs, and not exercise right before bed.
It is recommended that you get your daily workout in before midday to give your body enough time to power down before you go to bed. You could also create a relaxing pre-sleep routine to prepare your brain for sleep, such as putting away all devices 30 minutes before bed, turning off the lights, and reducing physical movement. This will cue your brain that you're getting ready to sleep.
Breathing exercises before bed are also effective in preventing hypnic jerks. Deep breathing exercises will help to slow your heart rate and help you enter a relaxed state for a good night's sleep.
While they can be alarming, hypnic jerks are totally normal, harmless, and nothing to worry about. They are fairly common and lots of people experience them from time to time. They may be caused by your brain reacting to stimuli or having trouble interpreting your sleep patterns, so you can help it by developing healthy consistent sleeping habits. Cut down on alcohol, caffeine, stimulating drugs, and exercise after midday to give your brain and muscles enough time to relax come bedtime. If you're still concerned about these sudden muscle movements, you should talk to your doctor about them.
Myoclonus Fact Sheet | NIH: National Institute of Neurological Disorders and Stroke
Why Do I Feel Like I’m Falling or Twitching As I’m Falling Asleep? | Cleveland Clinic
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