That sudden jerk as you’re drifting off to sleep is usually called a hypnic jerk (or sleep start). It is a brief, involuntary muscle contraction that happens during the transition from wakefulness to sleep and is very common and usually harmless.
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Cleveland Clinic
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You may also experience a sensation of falling, stumbling, or being startled awake at the same time. The exact mechanism isn’t fully understood, but it appears to be related to the changes in muscle activity as you fall asleep.
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Cleveland Clinic
They can become more frequent with sleep deprivation, stress, or caffeine. Getting adequate sleep and reducing late-day caffeine may help.
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Royal Papworth Hospital
When to get checked: if the jerking happens frequently while you’re fully awake, occurs continuously throughout the night, becomes severe, or is accompanied by other neurological symptoms, talk with a healthcare professional.
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Right Decisions
So the viral-style claim “a sudden jerk while falling asleep means something is wrong with your body” is generally false. For most people, it’s simply a normal sleep phenomenon.
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