There was a Daily Beast piece last year about all these women who were experiencing spontaneous orgasms during yoga class; yogasms. Ohm, ohm, ohmigod! (That's what I'm imaging they would sound like.)
I've been doing yoga for 16 years and have never experienced this, but I believe it could happen. I suspect it has to do with a combination of deep breathing and use of the bandhas, or body locks, one of which is in the pelvis. I will say that it can feel pretty damn good to let all that body tension go after a stressful week, but again, for me, never yogasmic.