It’s like we feel like we’re falling
In: Biology
It’s called a hypnic jerk. It’s a fun little quirk left over from when our ancestors slept in trees.
Basically as your brain is falling asleep it goes through a checklist of things to do, one of them is to engage the “OH SHIT WE ARE FALLING OUT A TREE” alarm. Sometimes we fall asleep in a weird position and that accidentally causes a false positive to trip that alarm, which causes us to snap back awake.
Hypnic Jerk.
In short, your brain sends a quick jolt as an alert mechanism, thinking you are falling when you’re only trying to sleep.
This is common and it has a name: a hypnic jerk or hypnagogic jerk.
Kind of crazily, scientists don’t actually know why this happens. It happens more with stress, caffeine, or evening exercise, but we don’t know why it happens to begin with. One theory suggests it’s an old primal instinct related to really not wanting to fall out of tree branches when our ancestors lived (and napped) there, but there’s no consensus on that or any other proposal on why it happens. Could just be a random side effect of the way the body shuts down to sleep. More info here:
[https://en.wikipedia.org/wiki/Hypnic_jerk](https://en.wikipedia.org/wiki/Hypnic_jerk)
It is called hypnic jerk. It is not entirely clear why it happens but it is thought to be related relaxation of muscles as we go to sleep.
One hypothesis propose that the sudden relaxation of muscles just as we go to sleep causes the stiff body to suddenly go limp, which generates the sensation of falling. Another hypothesis suggests that it is an archaic reflex from when our primate ancestors slept on trees. This reflexed functioned to ensure that a tree sleeping primate was on a secure location before sleeping, so if the brain was uncertain, it would wake the individual to reposition the body. Falling sensation probably functioned to remind the conscious mind that the reason for waking up was the risk of falling. Based on this hypothesis, this reflex can randomly kick in humans under stressful conditions. I have read that some evidence for this hypothesis comes from the fact that hypnic jerk is a lot more common if we sleep at unfamiliar locations, or if a person is sleeping very close to the edge of the bed etc.
Gemini states this: “Relaxing muscles during sleep: As you fall asleep, your muscles naturally relax. This relaxation might be misinterpreted by the brain as a falling sensation, triggering a jerk to ‘catch’ yourself.”
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