Just before falling asleep, why does my body sometimes "jerk"?

Answer 1

Twitches while falling asleep are called hypnagogic myoclonus, myoclonus being any sort of involuntary muscle spasm and hypnagogic referring to sleep. The twitches occur during very light sleep as the conscious brain gradually relinquishes control of the motor functions. Often they're accompanied by a sense of falling, or the feeling that something is flowing through the body, and sometimes people will experience vivid dreams or hallucinations.

It's not known exactly what causes the twitches, but they appear to be associated (although by no means invariably) with (a) anxiety and (b) some faint stimulus, such as a noise. The twitches have been induced in test subjects who were instructed to push a button whenever they heard a low tone. When, as usually happened, the subjects nodded off after a while--you know how exciting psychology experiments are--the tone would often cause a subject to twitch after a lag of a few seconds.

It's conjectured that the subjects consciously knew they were supposed to stay awake, that they fell asleep anyway, and that the tone jarred the semiconscious brain into trying to scramble itself into action again. That would explain why you experience the twitches during boring lectures. It's thought that at times the stimulus can be purely involuntary, such as a dream.

Answer 2

It's an innate response the brain makes. As you fall asleep there are a lot of changes that occur in the body. Metabolism and heart rate slow down for example. Your brain, being all powerful, observes these changes and suspects the body is dying or injured. So it causes this jerk to see if you're still alive. It's very uncommon to happen while you're awake (because everything is at the right level) but it can happen and is a symptom of some neurological disorders.

Answer 3

Why you are describing is called a myoclonic jerk. It's an involuntary muscle spasm just in the early stages of sleep.
During sleep, your brain actually paralyzes the voluntary skeletal muscles of your body to some degree. This is supposedly some evolutionary protective mechanism when our ancestoral critters were dwelling in trees.
Sometimes, on the edge of sleep, this hiccup in the system occurs resulting in a myoclonic jerk which wakes you up, and it's annoying.
On the other hand, the opposite is much more horrible to contemplate. Some people experience a disorder called sleep paralysis, where they wake up, but the mechanism of their brain is faulty, so they cannot immediately resume voluntary control and they lay there, wide awake but unable to move or speak. Very scary!

Answer 4

It could be spasms if you are really tired. That happens to me but only when I have stayed up for a really long time and need sleep badly or if I didn't get enough sleep the night before.

If you find yourself jumping up somewhat violently, it could also be related to Post Traumatic Stress disorder. Sometimes your sub-conscious slips into a bad memory and makes you jump out of the fight or flight response. I have worked with Psychologists who have suggested that I suffer from this and since working with them, I have noticed a big decrease in the number of times I jump (or bolt) out of trying to fall asleep.

Answer 5

I don't have an answer for you, but I wanted to let you know you're not alone, I do the same thing.

Sometimes I'm just beginning to dream and something happens like I trip, so I jump and wake myself up .. but sometimes my body just jerks for no apparant reason.

Answer 6

That is called hypnagogic myoclonus and it happens to a lot of people. It is often accompanied by a sense of falling. There really isn't a clear reason for it happening, but I know that it often happens to me when I am falling asleep while trying to stay awake, like in the middle of class.

Answer 7

The best answer in my opinion is your body is falling asleep before you are. This cause you to jump like if you was coming out of some sort of in-volunteer fainting. It's quit scary, like if you went with it you feel like your would die because you loose control of your body. it's quick but quit intense. but its just your brain keeping your body from sleep walking while you dream or not. i would suggest changing you sleep position. or put you body in that position that you know would keep you from this heart pumping scary experience.

Answer 8

It is caused by a nerve impulse cascade through the body. It commonly happens when in the state of relaxation.
It is like all the nerve impulses in your body synchronise at once and gives you a little jump. Feels funny when it happens like an electric shock.

Answer 9

Your body jerks because of a reduced blood flow to that limb. In effect, your brain is responding to the slowing of your heart rate, reduction in blood flow as if you were dying...it sends a signal to the nerve endings to spasm that limb, thus the quick twich.

Answer 10

Yeah. it feels like your body is suddenly falling, or being launched in a certain direction. It always scares the hell out of me!

My fiance noticed it when that happened to me on time. He was like.. did you just have one of those "jerk" things? Apparently I thrashed when it happend.