To this day, my heart rate is elevated at every exam, even though I know I'll stay fully clothed. If the doctor or nurse taking my pulse mentions it, I just say it's anxiety over the blood draw, since I'm so squeamish, even though I know that's not the reason.
It's been that way since I was a teen, when I had to undress for my physicals. But I don't think it was a worry about being naked during the exam itself. I never had a problem with the pediatrician pulling down my undies for him and my mom to see how my penis and testicles were developing. But when I started getting chubbier in my early teens, I wouldn't even want to go to the swimming pool anymore, or do anything else with my shirt off. So the anxious part of my annual physical was always after I had undressed to just my tighty whities and was sitting on the exam table waiting for the nurse to take me back out into the hallway to the shared scale for height and weight. I never knew who would be seeing me in just my undies in that hallway. Oddly, I never looked forward to it as an opportunity to see other kids in just their undies, even though that definitely was a curiosity for me.
I remember before my teens once seeing an older boy as tall as the nurse in that same situation, so I knew as I got older, they'd keep treating me the same way. It was probably 50/50 over the years between it being just my nurse and me in the hallway vs. seeing other kids / being seen by others while I was being weighed.
The last time I was seen by anyone other than medical staff and other patients was when I was 14, and I saw a boy I assumed to be a senior (he was wearing my school's "letter" jacket) being led into his exam room with his mom. He looked as embarrassed as I was, and she just smiled at me. I later found out he was only a year ahead of me in school, so probably 16 at the most. At 15, when I was at my chubbiest, it was fortunately just the nurse and me.
At 16, as we entered the hallway, I heard another boy in the next exam room complaining that he was too old, and his nurse saying that even older boys are weighed in just their undies. As my nurse had me get on the scale, the other boy finally relented and came out into the hallway, and he definitely was not a teenager yet. When my nurse had me get off the scale and lock it so I could stand back on it, with my back to the scale so she could get my height, the other nurse asked me how old I am. I said 16. She then told her patient, "See? Even much older boys are weighed the same way." After that experience, having the doctor pull down my undies several minutes later in front of my mom didn't even register on the anxiety scale.