I was hospitalised back in 2004 for three and a half weeks, in two hospitals (I was sectioned). The first one I was there for three-five days. I was treated slightly differently from the others because I was going to be moved to my local hospital. So I had my own room, I was allowed to keep my phone. My clothing wasn't searched because I hadn't expected I would be sectioned and I had only what I was wearing and they didn't search me. I can't remember it properly now but I know we weren't watched all the time, we were allowed to have baths and visit the toilet unsupervised, etc. _Sky is right about having to wait inline for meds, and they make you take them too, no protests.
When I was moved to my local hospital, it wasn't as modern for a start, and the food was horrible (care of the NHS). The supervision wasn't good either. If I'd seriously wanted to, and if I could have dared to properly attempt it, I could easily have hanged myself there - they didn't take away the girdle of my dressing gown, and the beds had metal frames round them - all too tempting
I was also allowed, since I was feeling antisocial, to go to the sink rooms and go to the end of the cubicles there and read for hours before people came looking for me. I was also caught cutting once, I nearly got away with it but they saw the blood on my arm, and *then* they confiscated my razor and made me empty my drawer and hand in my sharps (idiots). But other than that they were fine, and friendly, and in general we were allowed to mix with other people np. One night I was feeling very anxious and upset and I couldn't get to sleep for hours and hours, and I got to talk with the night nurse, and she was really friendly and calm, and helped me. But yeah. I think that in general, mental hospitals are places to avoid unless you have to go there. But I think since you want to go in voluntarily, you should see if it's possible to look around there first and ask them how they treat their patients, before you decide to commit yourself. Consider your own mental health too, when I was at the first hospial there was an upsetting incident when an old woman there suddenly went mad when she was in the little kitchenette, she grabbed a knife from the drawer (thankfully a food knife and blunt) and tried to slit her wrists, screaming, 'I want to die, I want to die!' She was quickly subdued and she did not hurt herself but it is upsetting to watch such things.