Is it normal to be turned on posing nude?

I am almost 18, in my first year of college. An elective I signed up for was sketching and painting. During the second meeting the instructor asked if any of the female students would be interested in or willing to pose nude for the class. I found the idea exciting but said nothing. The instructor asked several girls and they said no, but then he asked me directly and I stuttered like you mean here, this class, totally naked? He nodded yes, I asked when and he said beginning today for this and probably onecor two other classes. I numbly said I'd be kind of willing to try and he said super, why don't you get undressed so we can have a look at you....I nodded and asked where. He said they had no dressing room so I'd have to undress there. Gawd, in front of everyone? There were about twenty in the class. I said ok, was in the front of the room with the instructor. I began unbottoning my blouse and took it off, put it on a desk, then reached behind andcunhooked my bra and slowly let it come off. I was bare breasted and my nips were hard from the cool air hitting them. The instructor smiled, students were staring. I was red faced, but felt excited with everyone looking....I still had to get my skirt and panties off, so there is more to tell.....
Is it normal to be turned on in a situation like this?