I read in a book once that the zone 10-20 minutes before sleep where you're kind of transitioning is a kind of altered state of consciousness, and that Edison used to utilise this by, during working sessions, sitting in a chair with a glass bottle in his hand and dozing off to sleep. He'd make progress in his thinking in this "special zone", keep moving through it to sleep, drop the bottle, smashing it on the floor at which point he'd be awoken and would bring back what he'd achieved into the "real world" and press on.