Your therapist is right. if its what you want, and you want it bad enough, then you will be the one to go to therapy, if you are the host personality.

If you find that you have no control, try, and try again. Maybe you miss this session, but practice makes perfect. You do have the ability to control who comes out, and when. It just takes practice and time.

Relaxing helps, as best you can. get plenty of rest. and try telling the other personalities that you are taking this session. (they dont have to hear you, just say it to them)

I hope this helps.