I'm sure I'm not the only one who's experienced this and I'm sure there's a simple answer. Occasionally, including today, I was attempting to take a nap when all of a sudden my arm kicked into the air and slammed into the bed. My heart dropped and probably increased in speed by two-three times the average rate. I'm not sure if I'm asleep, sleep paralysis, some kind of in-between stage or what but it always happens so fast and I'm always in a state of shock when it's over. It's not limited to my arms but only occurs in my limbs. Any ideas or insight would be appreciated.