I would go into the hospital and see if I couldn't get a new or different perspective on things as well as break the cutting habit and maybe even a little stress rest. I use to stand on the dresser in my bedroom and look around my room, looks wholly different from that angle :-)

It has to feel messed up to be getting ready to take a job as a therapist and worrying about whether you should go in hospital or not. Maybe you can journal the experience and it will come in handy in your work one day. I would try to think about it a little like journalists do who are embedded in a gang or prison or war, etc. Right now you may be having difficulties but you're also only at the beginning of your "real" training and work, etc. Bipolar ain't easy to get under control all the time. My billionaire uncle had it and lost everything, got out of a hospital stay and made it all back. You will still be you with your personality and skills and knowledge, etc. That you have an illness that's difficult to treat is not about "you" personally and what you are doing with your life. It doesn't reflect on you as a therapist.

Think of Jamison and the therapist with the really deep depression who needed ECT, etc.