BMI is going to be replaced by the midrif measurement. A lot of practitioners are losing faith in the BMI chart because of enormous irregularities in its accuracy. The waist measurement (half way between the bottom of rib cage and hip bone actually) is far more accurate in warning the doctor of impending issues with the heart and circulatory system. (>37" by the way)
Talk to your AME about your "white Coat Syndrome" (fear of medicals/doctors tests). They have all been trained to recognise it and take it into consideration. For instance they (should) chat to you to assess your behaviour. If they sense anxiety/irritation etc they will expect higher than normal BP for instance or a different ECG print out. They have seen it all before.
I suffer enormously from it and the longer the wait in the waiting room the worse I get! I have had a frank and honest chat about it to the doc and he and I both know that future visits will prepare for this change in 'arousal state'.