Idk how i know but sometimes, when i am sleeping i feel my body or limbs shake like i am having seizure. i can't stop it or wake up. what is happening?

Shaking at night: I can't tell you what is happening, but i can tell you that it is not a common generalized seizure because then you would be unconscious. There is a common disorder that occurs at night called myoclonic jerks, but these movements are sudden and intermittent jerks of the arm and/or legs. They do not tend to go on all night. I would consider causes like stress or drugs.