Self-torture

There are some people who torture themselves.
I just don’t understand why they do so.
They must be sick.
To tell the truth, I am one of them.
But my torture is a little different. I torture myself during sleeping.
I squeeze my wrist by other hand, bite my lip hard or hurt my leg by kicking.
I do so without knowing in sleep.
This is also a king of sick. I think that this happens by a sleep disorder.