Is it normal to orgasm while riding a horse?

I've never told anyone this before, but while I was at college, I studied equine, so some of the stuff we did was taking care of horses, feeding, grooming, mucking out, etc. And one of the things we did was horse-riding. Well one day while riding a horse in the arena, I started to feel really turned on, well it was only the physical sensation of my vagina rubbing on the saddle in my tight jodphurs. I started breathing heavily and actually orgasmed. And there were people there watching. I'm so afraid they noticed. But anyway is this normal? Is it just me? I feel weird about it.