How come you fall asleep without knowing it?

Question

How come people cannot tell when they're falling asleep, I can never remember exactly when I fell asleep, its weird..

Answer 1

If you continually access your conscious processors which perceive the arrow of time, you will tend to only fall asleep because of weariness, rather than an autonomous sleeping state.

If you wish to determine the time you go to sleep, you won't go to sleep until you are too tired to worry about what time it is.

Answer 2

Because youre already sleeping.. when you close your eyes you have to know that youre sleep or already dozing off.