About 70 percent of people occasionally experience the sensation of falling just as they drift off to sleep—but no one knows exactly what causes them. These involuntary muscle twitches in the arms, legs, or entire body are called hypnic jerks and they’re very common.
The hypnic jerk occurs when the muscles, usually in the legs (although they can be observed throughout the body), involuntarily contract quickly, almost like a twitch or spasm. While the whole phenomenon is not dangerous and usually does not bother people, there is little research regarding what causes these jerks and how they can be avoided. However, there are two possible theories about it:
1. Hypnotic jerks are a result of the natural downshifting of the nervous system that occurs as you’re falling asleep: As your breathing and heart rate slow down and your body temperature drops, your muscle tone shifts, and these twitches occur during this transition.
2. As you’re drifting off to sleep, your brain misinterprets the relaxing of your muscles as a sign that you’re actually falling and signals your muscles to tense up, in order to protect you.
The most common assumption is that hypnic jerks are merely a symptom of our active physiological system finally giving in to relaxation.
While hypnic jerks are usually nothing to worry about, in some extreme cases they can be frequent and intense, thus cause stress and keep people awake, preventing them from entering the normal sleep onset process.
In these cases, people should cut down on caffeine (or other stimulants) and/or vigorous exercise in the evening and high stress and anxiety levels at night. All these are associated with an increased chance of a spontaneous hypnic jerk and should, where possible, be avoided.
Check out a video below of a case of an intense and frequent hypnic jerk.
