For two weeks back in high school, after a very... serious bout of depression. I hated it, and wound up lying about my progress so I'd get the okay to go home early. (I'm much better now, through the help of a competent therapist and my own determination.)
They're not the most therapeutic places to stay and the nurses act like you're a nuisance, and I hear that from most people I know who've spent time in these places. There was only one window in my ward that wasn't permanently covered by blinds, and we got yelled at if we looked out it for too long. Another time I was passing by when two girls started fighting, and after they were pulled away I was told to sit down or I'd have to go to bed early, even though I wasn't involved.
One minor event in particular has always bothered me. Every day at group therapy, we had to state a goal for the day. Everybody always fell back on the standards: "Maintain a positive attitude" and "Focus on my therapy." Now one day I decided to say, "I'll try to stay in a good mood." Everybody, including the therapist, shot me down and told me to pick a real goal. So maintaining a positive attitude, which is easy to project falsely, is okay, but actually attempting to stay upbeat for real is not? I never got that.