You may think that tying in bed until 12 o'clock on the weekend is good for you but you are wrong your biological clock tells you when you are tired it also tells you when to wake up and if gets confused and you feel even more tired A particular chemical is responsible for waking you up it starts to work from 3 or 4 a.m until 11a.m. If you sleep any later than this you prevent the themical from working which in turn prevents you from feeling wide awake