Help! I never realize I am falling asleep!

[Echorlen]

Whenever I am in bed trying to fall asleep, I never realize I am drifting off. Last night I was trying to somehow induce LD by repeating a sentence over and over (question: would this even work?). I'm repeating it in my head, but without even realizing it, I had fallen asleep. Soon, I had woken up in my bed. I can slightly recall my dream, but only a moment of it. I don't remember ever falling asleep. How do I learn to realize I am falling asleep? Is there some kind of trick I don't remember reading about? Thank you. EDIT: Is realizing you are falling asleep necessary?