This is a pretty long story, but all the details are important.
When I was 16, just before I went to sleep or went to bed, I would have these sort of jerking and twisting motions in my limbs (and head).
I had been aware of this involuntary muscle movement for quite some time and it didn't hurt or anything. When I started working in a restaurant, with dark background, flashing lights, occasional loud noises, ...