Well, on those rare occasions when I actually get to sleep in my bed, I sleep deep and long and typically restfully, with the benefit of actually being prone (as opposed to "slumped in a chair"), and various bodily systems, typically stymied by my spotty sleep in non-prone postures, really kick in. Most noticeably, my feet and ankles, which are typically fairly swollen, end up looking like popped balloons, the liquid build-up having had a chance to drain out. Also, nagging muscle pains tend to go away, again, no doubt due to the inefficiencies of trying to drain off lactic/uric acids from over-worked muscles when simply passed out somewhere.
Now, all this would be lovely if it wasn't for the fact that after getting a long (I was probably out for 10 hours, easily twice my typical sleep), deep, prone sleep I wake up feeling like somebody had beaten my kidneys with a baseball bat over night. This will typically go away after an hour or so of morning activity, but it's never a "pleasant morning" after that sort of sleep. Needless to say, the kidneys get the brunt of all that "draining", with days and/or weeks of acids, etc., getting flushed out overnight, so it's no surprise that they'd feel like crap in the morning, but it's a pretty nasty "trick" to know that a "good restful sleep" is going to rather predictably end that way.
I suppose that if I ever managed to get into the habit of getting 8 straight hours of lay-down sleep a night over extended periods of time, this would eventually not be a problem, although the last time I had multiple nights of long prone sleep (when we were out at Starved Rock State Park a month or so back, where there was "nothing to do" at night but sleep), it was the same deal every morning. It does, however, seem to be somewhat counter-intuitive that I feel better on mornings when I've slept at my desk from 2-6am than when I've gotten 10 hours of bed time!
Hey, I told you this one was gonna be "TMI"!