this can happen to me when i have been deprived of regular sleep for many days..i am just about to drift off into dream land when i got this involuntery body spasm .or quick body jerk that wakes me up fully alert and no longer drowsy..a couple of time i recall just drifting off and waking to a really loud bang or snapping sound that seems to come from inside my head that also wakes me up with a racey heart aand fully awake and aware...how common is this?