Can you put yourself in a hospital and get out when you feel like it?

This isn't normal for someone to do. It causes other people who are hurt to wait even longer because you're in there taking up space for no good reason. Which is totally unfair. Additionally, why would you want the bill? Unless you're on free medical care and go there for every sniffle.

If you meant a mental hospital, no, you can't get out when you feel like it. Doctors will release you only when they feel that you are not a threat to yourself or anyone else.