Okay so every once in a while I will be drifting off asleep for a couple minutes or it may have been hours idk but then I will wake up kind of hearing a boom and feel like im falling onto my bed and it startles me so bad but then I realize I am just in my room and fall back asleep I have talked to friends and my mom and sisters and other people and they say its normal and it happens to them too. Does anybody know the reason for this with out using big scientific words because I just want a simple answer of why it happens. thanks