YANBU, I was (and still am largely!) exactly the same as you. I couldnt even go sit in the waiting room without having a panic attack and needing oxygen!
Last year though I was lucky enough to be promoted into a job which came with free Dental Insurance. So I thought, right, my teeth are in a horrific state and now is my chance to go private and get it all done - it's free afterall!
So I found a lovely dentist who completely understood my fears. I had to ring around a few to find this one though, so many dont want to know when you're as nervous as me!
For my first appointment, I went to the GP who prescribed me 1 2mg tablet of Diazepam. I have to be honest - it did nothing! I went to the appointment and was still petrified, so much so that the dentist wouldnt even do the check up! He gave me a prescription for some 5mg tablets and told me to take 3 before my next appointment - 1 the night before, 1 on waking and 1 an hour before the appointment.
I cannot begin to tell you how fantastic they are! I have now finished my course of treatment (it's taken me about 18 months), and although I had some done under sedation, most of the appointments I got through with just the Diazepam. I still couldnt go now without the tablets but its amazing how they calm you down. I also used a tapping technique which helps calm you (google it), a lovely MN'er told me about it before one of my appointments and it does work! Although whether or not it would work without the help of Diazepam I dont know
Anyway, please ring around, find a sympathetic dentist and go. Ask him if he'll prescribe you something to calm you - I wouldnt bother asking the GP as apparently they dont like prescribing valium type drugs just for dentist appointments!
Good luck, it is tough but believe me, it is SO worth it in the end. I'm so glad I did it and will now go regularly for check ups!