You will likely have to get naked in front of a nurse, but in my experience, they try to be sensitive and don't touch you or pat you down. You may have to cough and squat, but that varies by location.
They will go through the belongings you bring and take anything that might be risky to you or another patient. Expect to get the strings yanked out of your hoodies and waistbands, your shoelaces confiscated and perhaps even your hair care tools locked away with access by asking each day. It's not just about you at that point. Since room doors are not locked, they need to take anything that any patient might be able to use to self harm.
The best way to avoid some of this unpleasantness is to send home any of this stuff with your family before you get to the ward.
You may also be seen by a nurse to assess any medical needs you have. These might be anything from high blood pressure to wound care from a previous attempt. That's how you get your medical needs met. so if you need something, speak up.
One place I stayed did not allow me my stuffie because they'd had a previous bedbug incident and only allowed their bedding, sealed in plastic, and nothing else. That really sucked since that's still my comfort if my husband is not around.
Mostly, you'll waste a ton of time sitting around. Depending on the way the program is structured, you'll attend "groups" meant to be therapeutic that cover DBT, addiction issues, mindfulness, deep breathing and the like. There is usually lots of coloring - especially mandalas and other thing they think might be calming and/or spiritual for you.
You won't see the psychiatrist much. You'll mostly interact with the staff and other patients.
It will go a lot easier on you if you stop thinking of it as "jail." Yes, it sucks, and yes, you can't just walk out but the goal of most of these places is to get you out as quickly as possible, not to keep you as long as they can. It's much safer to have someone to talk to if you're coming off Prozac to begin with - SSRI withdrawals can be a bitch. At least inside, you can get anti-nausea drugs or maybe even a benzo to help you come off, even in the middle of the night.
Rather than act as if the staff were your "jailers" or the enemy, try to just take it one step at a time and go along to get along. Being combative - even being a smart ass - can lengthen your stay and keep you on short checks. Checks are just that - the staff will check on you every 5, 10, 15, 30 or 60 minutes depending on their policies and your behavior. This includes while you are sleeping during the night. You're less likely to wake up if they can see you from the doorway, so you may want to sleep with your head pointed that way. To get off short checks, you need to be cooperative.
Sooner or later it seems like most of us wind up going for a visit. It won't be fun, but you might gain an insight that is valuable (I did on my last visit) or at least catch some needed sleep. Hang in there and remember - this, too, shall pass.