A hypnic jerk is when you're falling asleep and you dream something which makes you wake up. In my case I usually dream I'm falling off rollerskates, which is weird because I don't think I've rollerskated for about 20 years. I think this can also be called a Myoclonic shock, but I'm not sure. I was glad when I found this out, because I always wondered if there was a word for it.
Hypnic Jerks are a kind of Myoclonus, and myoclonus is the medical word for muscle twitching.
Here's a good one though - there is another type of myoclonus which affects us all from time to time... yep... hiccups.
booya.
