Why does the human body jerk/shock itself awake sometimes while trying to sleep?

Question

Why does the human body jerk/shock itself awake sometimes while trying to sleep?

In: 2959

Answer 1

I read a long time ago that it may date back to when we slept in trees, and that a sense of losing any amount of balance (for whatever reason) would jolt us awake so we didn’t fall from our branch.