I have testicular pains on and off for years, so I had my share of genital exams. some of these exams were done while lying down and some standing up, I guess it depends on the doctor.
Usually those exams are not much "fun", they are either very short or quite painful (usually when preformed by male doctors). However, my general doctor (female) once examined my testicles while standing up. She's very thorough so it lasted a bit longer then most exams, and she was very gentle so it actually felt nice.
I started to get an erection, but since I really like this doctor and see her often, I tried to avoid getting a full erection so I stared at the ceiling and tried to not to think about it. It was hard because when I sneaked a peek down I saw that her face was very close to penis, and I think she wasn't wearing any gloves either. After she finished with the exam I immediately pulled my pants up, and it was lucky because shortly after I had a full hard erection.
I'm sure she noticed my penis getting larger during the exam but she didn't say anything and neither did I. I acted as if I was embarrassed even though I wasn't, because I didn't want her to think I'm some kind of pervert and enjoyed it (which I guess I kinda am :).