As a point of clarification, since your gender is shown as "male", you were a masseur, not a masseuse. A masseuse is "a woman who performs a massage; a female masseur."
I played football in high school and college. In my middle-late twenties I developed recurring lower-back pains, most probably a result of playing-days injuries. There have been times when I go monthly for adjustments with a chiropractor for relief or prophylaxis/prevention. Two chiropractors had associated masseurs (one a professional masseur, the other a trained physical therapist.) With both of these, I was either fully clothed or with just the shirt removed, and the massages were only for 15 or 20 minutes, so erection was never a problem.
But subsequently I took to getting frequent massages, usually from masseurs. In these "full length, complete" massages, greater degrees of disrobing occurred, and, yes, I frequently got hard. One of my first masseurs, noticing my embarrassment, commented, "Don't worry, it happens with most guys." Usually I was tenting a towel or covering of some sort, but occasionally not, and sometimes I poked out the side. At first it was embarrassing; I was afraid he'd think I was gay or something. But with time I stopped worrying and, frankly, found it pretty erotic. I never was offered a "happy ending", probably because the masseur could tell I would be bothered by such an approach.
There is one massage episode which comes to mind. I once went with a friend (actually my boss at the time) to get a steam bath and a massage. He stuck his head in while I was getting my massage to let me know he was done and would be waiting in the lobby. Needless to say, he got a good, though brief, look at me at full staff. . . which isn't saying much: I'm hung like a chipmunk. No big deal, he'd seen me in the showers. But now whatever suspicions he had about whether I was possibly one of those surprising "telescopers" or not were answered; I wasn't. However, he never said anything about it afterwards.
