I become aware of my body growing heavier and stiller and somehow farther away, to the point where I know to move them I’d have to first wake back up; of the view behind my eyelids becoming darker and gaining a sense of depth; and of the sounds I still hear becoming gradually more surreal. It’s at this point that, if I have something in mind, I can usually start to construct what I guess is a lucid dream, or at least arrange different elements that I want to show up in my dreams later that night.
I don’t know that I’m ever aware of a “moment” that I’ve fully fallen asleep, though I guess at some point there is a threshold, some line between waking brainwaves and sleeping one. I certainly don’t remember it.
On nights I’m having a hard time falling asleep I’m not aware of any of this. I’ll just be laying in bed feeling fully awake, and then I’ll wake up some random time later, (maybe I got a full night’s sleep, maybe it’s in the middle of the night), surprised that the time has passed.