From wiki...."A hypnic jerk, hypnagogic jerk, sleep start, sleep twitch or night start, is an involuntary twitch which occurs just as a person is beginning to fall asleep, "

I must be suffering a worse than usual version of these. The ones that happen as I am falling asleep will wake my wife up. They also wake me up enough that I can not get to sleep. Any twitches that happen after I have fallen asleep do not bother her.

They also can happen during the non-REM sleep cycle. Some suggest that they are a system that causes us to change positions during sleep. If they cause me to change positions, I end up manifesting ballistic movements where my arm or leg will fly to the extreme of its range of motion. I now take gabapentin to settle my body down.

Anxiety makes them worse so they can lead to a scratch-itch cycle where they cause the person to wake up causing anxiety about falling back asleep resulting in worse twitching.