It's very very bland and boring there.
Imagine an office building but with a bed, table, and sink in it.
You're gonna wanna bring something to occupy yourself. They won't let you have electronics and they may not let you have pencils/pens(thankfully, the one I went to let me so long as they kept the pencils/pens in their possession when I was finished with whatever I was doodling, but they were really reluctant.) Bring several books, because when the boredom hits, you will feel it quite hard if you have nothing to do. I just drew pictures and sang to myself in my 'cell' while I was there for the most part.
While there, you will probably do group activities, take a few written tests(not all that different from one of those online mental health quizzes, just longer), and talk to a few doctors that will ask you questions about your problems. And, if you haven't done it before, they may do the whole inkblot test thing. Not sure of the purpose behind it as I thought it was phased out of use, but apparently not.
The only time you will be forced to 'mingle' with folks is in group activities. I found a couple of them too distressing and I actually excused myself on one of them when I felt it was pissing me off.
Of course, it is of utmost importance to try to be as truthful as possible with the doctors there. I made the mistake of not doing that on my visit and keeping things hidden as I do with regular people. They're there to try and find out what is wrong to the very source and try to fix it.
Lunch is the best time. Hospital food has a reputation for being awful, but for some reason the food that was served in the psychiatric unit of the hospital I was at was absolutely fantastic.
To sum it up, boredom is the biggest issue. Otherwise it isn't bad.