your problem is called white coat phobia and is common, docs know about it
tell doc you have a reaction to your BP being checked which always raises it
it helps to take a list of what you want to mention to doc
or it can help to write a note for doc to read if you think you wont be able to explain your problems clearly
some are too anxious to stay in the waiting room, if so wait outside and get the girl to call you in when its your turn
in extreme cases, doc may come and see the patient in their car if parking space is nearby