nervous about cystoscopy

I am going to be having a cystoscopy in a couple of weeks to check for enlarged prostate, as the doctor wants to get a better view than the pelvis CT provides. I will be awake, but I know they use numbing gel to mask the feeling of it. The thing I'm worried about is how I'm going to react to being touched "there." Since it will remind me of having a girlfriend doing stuff to me, I'm worried that I'm going to be turned on and start moaning and groaning, or reacting to being pleasured, and getting an erection. I wonder if other men react like that, and if those reactions cause any problems.