because if you sleep more than like 8 1/2 or 9 hrs then your brain will get used to being in that state when you sleep so it doesnt function as fast...and your reflexs will slow down, but even if you didnt sleep one night or stayed up really late you still should only sleep like the same amount of time or maybe an extra hour. but dont sleep all day because ultimately if you dont sleep enough then you are tired but if you sleep too much then your senses (brain's reactions) will be dull which means they wont react as fast. but anyway the point is if you sleep to much you become lazy and you are tired all the time.