Not too long ago I was sleeping on the floor. When I started, I would have marginal soreness when I got up, but later I realized that despite having back pain sometimes before in the day, my back was feeling much better. Then I got in the habit of sleeping on the floor and it was no longer unpleasant. Getting up was better, too, because I didn't want to keep myself in a soft bed.
Lots of articles talk about this if you google it clearly:
http://urbanwomenfit...g-on-the-floor/
http://www.newhealth...-the-floor.html
http://www.md-health...-the-Floor.html