Has this ever happened to you? You’ve just dropped off to sleep but you suddenly jerk awake with an involuntary jerk. The scientific term for this involuntary muscular twitch is hypnagogic myoclonus. You can observe a similar reaction in people falling asleep during a meeting or in front of the TV. The head drops down and suddenly the person wakes.
If you experience hypnagogic jerks it means that you are ‘normal’ – well, at least as normal as the 75% of people who also experience the phenomenon. It has been said that being exhausted, uncomfortable, or even dehydrated contributes to the occurrence of a hypnagogic jerk. I’m part of the ‘normal’ population and I’ve never noticed a pattern. Please let me know if you have.
Often the hypnagogic jerk will be accompanied by a dream of tripping over, falling off a cliff, crashing a car, kicking a ball – there are a myriad variations. However, as true dreams are considered to occur only during rapid eye movement (REM) sleep, these ‘dreams’ could be more accurately described as hallucinations. It feels like you’ve been asleep for a lot longer than you have. Your brain has distorted time to explain the physical sensation.
But why do hypnagogic jerks happen at all? The rapid tensing and releasing of muscles is generated from the brain stem. This, the most primitive part of the brain is what keeps us our heart beating, our lungs breathing and it also regulates our sleep patterns It is the animal part of ourselves. When we sleep, our heart rate drops, our breathing slows and our brain stems panic. Well not always, but there is a theory that hypnagogic jerks happen when the brain stem misinterprets the normal slowing of bodily functions as… *ominous music* death.
Another theory, also related to our primitive selves, is that many evolutions ago when we lived in trees, it was advisable to make sure we weren’t going to fall and plunge to our deaths as we slept. The hypnagogic jerk functions as a last minute check that we are safe and sound. This helps to explain the rapidly generated dreams that usually accompany the physical shudder. Arms and legs are at the ready to grab hold of any strategically placed branches in response to the vivid sensation of falling.
So next time your bed-buddy laughs as you hit the ground with a thud, catch your breath and say ‘hypnagogic jerk’.