@ChrisF these decisions are difficult at the best of times when we are well prepared and well informed. It's not something that should be done on the fly unless there are very pressing conditions.
You are not welded to your current specialist. If you have lost any degree of confidence in them, see someone else. At least take some time to ask more questions. I can absolutely understand the desire to get whatever it is out of your tit but a week or so will not, realistically, make much difference if they are ambivalent about your diagnosis.
What ever this is, or isn't, you are likely to be in the system for a while, either in active treatment or under observation. Pick your team carefully--and yes, you can do that to a degree in the public system. Mxx