Would his regular pediatrician be able to provide the doctor's notice if you can't get it in time from the developmental pediatrician? It sounds like a good idea to get the dev. ped. evaluation. If he hasn't seen a neurologist that might also be a good idea. We found the neuro was better able to address muscular and motor issues than the developmental pediatrican was. It never hurts to make more than one appointment and to cancel later because as you said it can take some time to get in.
For the dentist, I'm wondering if there might be an option for him to stay with a friend while you go to the dentist alone and for someone else (a friend, a family member, a babysitter) to take him to the dentist. Anxiety really is contagious and it would be unfortunate for it to get worse for him. Another thought is that maybe one or both of you could benefit from cognitive behavioral therapy. Anxiety really is a treatable condition and the kind of process you are describing with escalating thoughts is something people can learn to become aware of and to at least some degree correct.
I think it would be appropriate to let the eye doctor know the technician was rude. They can't fix the problem if they don't know about it. Also, we've pretty good luck by being really upfront that the child tends to be anxious and we'd like them to go slowly and explain as they go.
Good luck!
