Sleep fit or hypnagogic shock
Just as you are about to fall into a deep sleep, you are startled awake by a shock going through your legs or arms. Or you are almost asleep and suddenly fall into a gaping depth. At least that’s how it feels, because in reality you are safe in your bed. What kind of strange phenomenon is that?
Such a shock or falling sensation in the phase between being awake and sleeping is called a hypnagogic shock or a sleep fit. Science isn’t sure what causes that crazy feeling, as extensive research hasn’t been done yet. There are quite a few theories.
Relaxed muscles
When you sleep, your muscles are relaxed. During the REM sleep, the phase in which you dream, the muscles of the limbs are even temporarily paralyzed. You do not fall asleep in one go and the muscles are not switched off in one fell swoop with a button. Brain parts fall asleep one after the other.
For example, it is possible that the brain areas that provide perception are still awake, while the part of your brain that controls your muscles is already asleep. The awake area of the brain therefore thinks that you are falling and reflexively tightens all your muscles to keep you upright. You experience this as a shock in your limbs.
Stress
Some scientists think the convulsions have something to do with stress, anxiety or disturbed sleep. They are more common when you are very tired or not comfortable. Another hypothesis is that as you fall asleep you go through mini REM sleeps in which you start dreaming and the muscles relax. This REM sleep while falling asleep could help prevent hypnagogic shocks.
Many people experience a shock before falling asleep. Usually you feel it once or twice a night. If you wake up again with that strange sensation, it may be annoying, but it can’t hurt. The shocks are harmless, at most you startle your bed partner.
Restless legs
If you keep experiencing a jerky sensation in the limbs that causes you to sleep badly, there may be more to it. When returning moving legs in bed, we speak of periodic limb movement disorder (PLMD) or in Dutch: periodic limb movement disorder.
In this sleep disorder, the legs and sometimes the arms make uncontrolled kicking and jerking movements while you sleep. While you may not even notice all that activity at night, it does affect you during the day. The movement ensures that you always wake up from your deep sleep, so that you do not rest enough.
PLMD often goes together with the restless legs syndrome (RLS), but it is not the same. With RLS you have an irritating, burning and itching feeling in the legs and sometimes also in the feet. The symptoms temporarily decrease when you move. PLMD is also more commonly seen in Parkinson’s disease, Huntington’s disease, some forms of ADHD, narcolepsy and sleep apnea.
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