There was a point in my teens where I had to attend monthly exams at a clinic for just over a year * and each time I'd have to undress fully right at the start. The dread of an upcoming appointment was only made worse by the nightmare of 'what if I get a hard-on'. Fortunately the reality of the situation and surroundings was so unerotic that it didn't seem likely in practice.
That is until the third or fourth time when I got an inexplicable erection on the way there that just wouldn't go down. Nor would it subside in the waiting room, and Sod's Law, there was no delay in my name being called for the exam to start on time. I undressed as slowly as I could, trying not to think about it but by the time I was down to my briefs I had no choice but to turn to my mom and mumble something about 'can I keep these on for now.'
It was the nurse who replied though, noticing the tiny tent in my briefs and breezily said not to worry, it happens a lot, it's natural, nothing to be ashamed of' etc - all the usual platitudes. So there I sat red faced and pointing straight up, waiting for the doctor to arrive.
They say that if you dwell on the things you fear then that can make them more likely to come about, maybe that was my problem here. But once it had occurred and I'd lived through it the thought became less scary if no less embarrassing and it never happened again, at least not to the same degree.
* I've written about this in my earliest posts on Zity, so look back through my posting history rather than me repeat the details here. Happy to chat or exchange messages from anyone who experienced similar or is just curious.