system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 what causes that falling feeling when you're asleep and you wake up in a jolt?

You know that feeling when you're asleep or almost asleep, and you start falling and you wake up like a split second before you hit the ground. What causes this?
gpt
Its called a Hypnic Jerk.  Its not currently known why it happens. The best hypothesis is that the various physical effects of falling asleep will sometimes  confuse your brain into thinking you're actually falling. Since your brain doesn't take chances, it sets off a reflex that would give you a chance of halting your fall.

But since it still being researched, any aspect of this hypothesis may become invalid at any time.