Effects of being bedridden...

And now my first-person present POV comes around to bite me on the butt...

My character has been bedridden for nearly four months (not due to illness or injury -- this is related to the no-pain torture question I posted a few weeks ago).  What I'm looking for is how he would feel when standing up for the first time and what kind of mobility (if any) he would have.  Would he need to learn how to walk again?  Would he even be able to stand?

Other details that may be relevant -- he's severely underweight, but has been getting nourishment for the last couple of weeks; there are no hospitals nearby and no means of getting professional physical therapy, though the character with him has had some minimal medical training; I have a magical closet (well, not really, but I can come up with a reason to have just about anything in it that I need) that can provide any necessary supplies to get my character back on his feet.

I've done searches on long-term illness (pressure sores! *shudder*) and bedridden (apparently a band?).