I've been a patient in mental hospitals more than once. And each time I've been in one of those places, I had to share a room with a roommate.
I have always had mixed emotions about it, as I sometimes wanted to have my own room all to myself.
But in general, I've found that having a roommate who has similar issues that I had at the time was a good thing. For example, sometimes if I was having a bad day and my roommate and I would start talking and chatting in a friendly way, it would make me feel better for a while.
So having a roommate while in a mental hospital can be a good thing, I think.