I've had a similar experience of being really worried going to a pdoc. It was still really scary every time. One thing that helped me was knowing that I I could still reach out to my T if anything overly scary happened with PDoc (and at times, when I was really in a bad space, scary things happened). I HATE talking on the phone. I stutter and freeze and brush everything off. My "professional" voice kicks in and hides everything. There were times though, that I was able to pick up the phone to call T... It took her a few minutes to figure out who I was (I couldn't even say my name in greeting), but just calling and hearing her voice helped...
about being scared of PDoc and letting him/her know: they have experience with clients that are scared of them and/or really gaurded. Hopefully, the PDoc you see will be gentle about it and help you htrough that fear.
I hope you can find a way to breathe through the appointment. As someone else pointed out, good PDoc's will not hurt you.