What does it mean when a body part falls asleep for sitting still to long and you get that tickling feeling? what's really occurring?

Pinched nerve: Many people think that your arm or leg going to sleep is from cutting off the blood supply. It's actually because you pinched a nerve. From being compressed too long, the nerve can't function, and causes your arm or leg to get numb and tingly. When you move, you're releasing the nerve, and the sensation of 'waking up' is from the nerve starting to transmit messages again. Great question!