My blood pressure goes sky high in the doc's office. I tell every provider that on the third try it. Comes down dramatically but they never do it three times. I watched a you tube once with a doc and blood pressure researcher from UCLA and he said that the best method for getting an accurate reading is to have the patient sit in a quiet exam room alone for 10 minutes. Feet flat on the ground with back supported them the nurse takes the reading. However, with the 15 minute exam slots this unlikely to be put into practice. When I think about your blood pressure scare during pregnancy it seems understandable that the docs office and the blood pressure cuff could trigger that fear and stress.
You might think about getting some treatment for that traumatic event. Something like EMDR or another of the great tools available. Another thing that you might try at home is a simple mindfulness meditation where you sit comfortably and focus on your breath. And when you notice a thought, simply return to notice your breath and repeat whenever you find yourself in a thought. The goal would be to tell the person who wants to take your BP that you need a bit of time alone in the exam room prior to BP. An even simpler technique to help with calming is to do simple deep breathing: gently draw air in through your nose with your hand on your belly and feel the air move with the breath, then gently blow the air out via your mouth. Even repeating this 5 times can be calming. You can even allow yourself to imagine your favorite place. A place that gives you a sense of calm and safety. I am not a doctor but these are things that I've tried that have been helpful. I hope that this is helpful. Good luck.