Freud, I believe wrote about the state between sleep and being awake. I often fall into that space and might go in and out of wake and sleep, while listening on my great rig. I have always thought it allowed me to experience things in ways that I could not while fully awake.
This is totally it. Its a strange but very cool place. I can't do it unless there are some sounds around to hang on and I am tired enough to even get there. Otherwise you are either awake or asleep. I sent this to another friend who listens to music and he said he hears elements/instruments that he doesn't notice as much when he is fully awake.
I didn't mean I use this to nap.