State Psych Hospital

I'm going to start doing some per diem work at a state psych hospital. I have one year of med-surg and no psych experience, except the little I did in clinicals, and that was at a drug rehab unit. I have no idea what to expect, can anyone fill me in. I don't know much about the population the hospital serves (all I know is adults, they have the "regular" units and the geri units), the typical dx I would see, or the types of tasks I would do. So ANY info is welcome!