If you don't feel comfortable about asking them, then yes, having a professional would be a good avenue. To be honest, I didn't tell my parents until after. However, the second time I went I had to talk with my fiance about it. I started off by explaining (in as much depth as I felt comfortable with) how I had been lately. I told him that I was suicidal to a degree that I couldn't handle on my own anymore. I needed urgent help to get it under control. Then I explained how a hospital might help.
When it comes to behavior, hospital staff usually, and are expected to have a high tolerance about that. This is just based off of my own experience, every hospital is different. Annoying, tends to come with the territory. I wouldn't dwell on that much due to the fact that I can guarantee that they are or have dealt with much worse. A hospital won't "kick" you out until they believe that you're stable and okay; or they're suppose to. You're the expert in your life, if they think you're ready and you aren't, tell them and explain why. Chances are that they'll keep you until you feel comfortable leaving; or at least they should. If they're a really good staff and hospital, they'll set you up with outpatient services after your stay to help ensure that you get the proper help you need.
This is how it was for me, but again, every hospital and staff are different. If you need it and want that kind of help, do it.