It is like a conditioned response. If you have your alarm set to a particular time, it becomes a habit, due to years of practice. Perhaps you begin to wake up and anticipate it occurring and that is why you wake up a few minutes before your alarm does. I do this all the time. If you need to get to school or a job, it is a good thing.
Some people do have an internal clock that seems to wake them up. Also, there might be a certain noise that occurs before your alarm is set to go off. I know what it is with me- my cat wakes me up!
I assume that your body gets used to having a specific amount of sleep. If you go to bed at roughly the same time, you might then wake up at the same time. This, of course, does not always work. There are plenty of people who are awakened by their alarms and still have a hard time actually getting up at that point.
same here and i agree with post#7. It's that desire, that internal want to wake up at a certain time that allows us to actually wake up at that time.
When i want to wake up at 5 in the morning to complete some very important work, i keep it in my mind before i go to bed setting the alarm and the next day i wake up at 4:55 just like you said. I think that it is because of that very internal want.
I have a similar experience too.
I believe that it is due to your internal clock as litteacher8 said.
Some people know the time without any sort of electronic device, because they have a feeling of time; the speed time passes. You are probably one of them.
You set your internal alarm when you decide to wake up at a certain time. That is what wakes you up before your alarm goes off.
You might think that you don't really have a feeling for time, but that is at daytime. I do not know why, but people tend to have a much better feeling of time when they are asleep.
since you repeatedly set an alarm clock and practice having sufficient sleep your body tends to develop a certain pattern of how to wake you up thats what most of us call body clock, roughly all of us who don't experience disturbed sleeping behavior develop consistent bodu clocks