My consciousness doesn't seem to disappear when I fall asleep, only my awareness of my bodies sensations. I often go to sleep reading, and the thoughts I'm having about the book I'm reading will continue for quite some time, even after my eyes close. I know this because I often startle myself awake by dropping my book. I also have similar experiences as I wake up, my consciousness slowly starts to incorporate my sensations of reality with the thought process that is continuously going in my head.