This Is Why Your Body Suddenly Jerks When You’re Falling Asleep


There you are, in bed, just ready to drift off to sleep and boom, you’re suddenly bolt upright, soaked in a cold sweat and wondering what just happened.

Well apparently you should be thanking your brain for taking such good care of you.

The sudden jolt you feel coursing through your body is known as a ‘hypnic jerk’, according to the Daily Mail, and it is thought to serve two possible functions.


The first line of thought is that the jerk serves to evaluate the environment one last time before going to sleep – ensuring it really is safe to shut your eyes.

Professor of Sleep Science at Northumbria University, Jason Ellis, expands on this while writing for The Conversation it may result from human evolution.

He said the jerk may have helped our ancestors:

…to check the stability of our body position before we went to sleep, especially if we started to fall asleep in a tree.

The jerk would allow us to test our “footing” before unconsciousness set in.


The alternate theory is that the jerk is a possible symptom of our active physiological system throwing in the towel and giving way to the urge to sleep – apparently the active physiological system goes down fighting.

‘Hypnic jerks’ remain somewhat of a puzzle, with further research required, but it is thought by Professor Ellis factors that could make them worse are: caffeine before bed, vigorous exercise before bed, or high levels of stress and anxiety.

Ellis also believes poor sleep patterns may have a negative influence, which is a bit of a bastard considering the jerks themselves are pretty much guaranteed to keep disturbing your sleep…