Unfortunately, I have a pretty good idea of what it's like in a wheelchair. Fortnately, it's only been for short periods of time (a couple hours), but I've spent much more time on crutches (in fact, I think I was pushed out of my last job due to being on 'em; had to use them for nearly 6 months once). The worst thing is that, half the time, I feel well enough to not need either one. As a result, people who see this think I'm faking it.
I've got two inflamed discs in my lower back. It puts so much pain in my hip (usually either one side or the other, but occasionally both) that walking is nearly impossible at some times. But, again, at other times the inflamation is such as to make me feel almost normal (some back pain's always there, though).
I don't believe I qualify for a DMV disabled parking placard, but I do qualify for a disabled parking placard at the school I was going to. Worst thing was, last spring, they were doing construction on campus and thus reduced the number of disabled and staff parking (the placard basically let me park in any spot on campus) to the point that they were all taken up by the time I got to school. There's a 25° climb for everyone who isn't staff or disabled, and even with this placard, I had to climb that hill last spring...almost put me back on the crutches.
Worst thing is, I'm only 21...I hope this condition doesn't exist the rest of my life.