I would think that it's virtually impossible to sleep while tripping. I know that the first time I tried MDA (that drug they used to sell over the counter at bars in the late 70's... the original drug from which MDMA is derived), I was at a party in San Francisco and getting ready to catch a ride home to Sacramento with a friend when I got a tap on my shoulder. I turned around and it was another friend who told me to open my mouth... which I did and he threw some sort of capsule in it and told me to swallow... which I did and proceeded to go home, much to the dismay of the friend who had given me the cap of MDA. Anyway. I fell asleep in this guy's car before we hit the Bay Bridge.... but on the bridge, the shit hit me all at once and I sat bolt upright in his car with the coolest body sensations! My friend looked over at me and said, "Did it hit you?" On that incident, I base my answer... no, I don't think you can sleep while tripping.
I don't remember where I heard it, and I think it was in reference to acid, but someone once told me that massive amounts of B-complex vitamins will bring someone down. I don't know what "massive amounts" would actually work out to, but B vitamins seem to interact with a lot that we ingest.
Unsubstantiated claims... but that's my input...