The hospital I have been in is a dual diagnosis, short-term acute crisis management facility, so most patients stay less than a week although most of my stays were more in the range of 2 to 3 weeks.

Patients were there for a variety of reasons. I was there for bipolar depression. I saw people there for anxiety, depression, self harm, suicidality. Some were there for substance abuse detox since this is a dual diagnosis unit. Some were clearly psychotic (but not dangerous in my experience). Some were there for a major medication change: I did that once as my doctor needed to make the change quickly and the med I was going on needed to be monitored closely.