We have our good days and we have our bad days. It all depends how you feel on the day. Human beings, in all other living things, have a biological clock which tells us when to eat, sleep and wake up.
If you unwantingly wake up early on weekends or have ever suffered from jet lag, it's probably due the effeffects of your biological clock in your body. The understanding of these clocks can be very helpful to you, for by doing so you may be able to learn to "set" them to wake up at a prearranged time, remind you of appointments or even help you to return to your car before the time expires on your parking meter.
If someone's daily biological clock runs fast, the person will tend to get sleepy early in the evening, but will be able to wake up in the morning with little difficulty. Exposure to the day/night cycle of the outside world will help him or her to reset his biological clock each day- humans being able to do this more easily than animals- otherwise he would go to bed earlier and get up earlier and earlier each day. Because of this need to readjust his internal clock, he is continually under pressure from the external world.