I sleep on just a folder up comforter in the floor pretty often. I have noticed that when I sleep on it, I get some back pain for about the first three days, but it feels like a "good" back pain if that makes any sense. Its almost like the floor is adjusting my back to where is should be. After the three days or so, I feel amazing.
Once I go back to a regular bed, I once again start to feel some back pain...unfortunately, this time is not a good feeling, lol.
I would love to stay sleeping on the floor full time, but I don't think the gf would like me abandoning her in the bed, and she definitely wouldn't have any part in sleeping on the floor