You know that point where you are going to sleep, then suddenly you dream that you are falling, or losing your balance, then you abruptly jolt awake, startled?
Don't you hate when that happens?
Now, researchers have figured out why this occurs, and have even given the experience a name. It's called a hypnic jerk. It happens during the hypnagogic state, (the time between being awake and falling asleep). The hypnic jerk is a physical response to a dream created by your brain that startles you into a wakeful state. It feels about the same as being startled while you are awake. It is quite harmless, as far as anyone knows. Roughly 65 percent of the population has had this experience.
According to the American Academy of Sleep Medicine, there is a wide range of possible causes for the hypnic jerk. These include anxiety, stress, and strenuous activities before bedtime. Also, caffeine, tobacco, and certain drugs (like Adderall and Ritalin) can trigger the hypnic jerk, or increase the frequency of the reaction. Another likely culprit is sleep deprivation.
Yet, most hypnic jerks occur in healthy people. Science refers to twitching in your sleep as myoclonus. About 90 minutes into your sleep cycle, a chemical is released that basically paralyzes the sleeper, so the sleeper doesn't get up and run around while dreaming. But if you are just falling asleep and already starting to dream, your body is not yet paralyzed, and so you jolt awake.
This hypnic jerk, also known as a hypnogogic jerk, a sleep twitch, a sleep start, or a night start, could be an evolutionary development that was designed to wake our primate ancestors before they fell from the trees.
The hypnic jerk usually happens when someone falls asleep rapidly after becoming exhausted. The brain processes the stages of sleep too rapidly, and “tricks” itself into thinking that the body's major systems are failing. So it responds with a burst of chemicals, which creates a dream that is guaranteed to wake you up.
According to a study of sleep disorders published for the Journal of Neural Transmission, the hypnic jerk occurs during the non rapid eye movement (REM) state of sleep. Most of us actually experience the hypnic jerk several times a night (less often in adults than children), but we tend to just fall immediately back to sleep and not remember.
The hypnic jerk is only a problem in rare cases. Marianne Middleton, clinical coordinator of the Lawrence Memorial Hospital Sleep Disorders Center, describes a “vicious cycle,” where the jolting keeps a person awake, and makes the person sleep deprived. As mentioned, sleep deprivation increases the frequency of the hypnic jerk. So the more worried and tired you are, the more sleep you lose, and the more the hypnic jerk will jolt you awake.
Severe twitching can be a sign of Parkinson's disease, Alzheimer's disease, brain injury, or a number of other factors. If your twitching is severe, see your doctor. But don't worry about the hypnic jerk.