I don't think horny is an emotion. Lust or need i think of as emotions. The difference between a desire to get my rocks off and my need for touch, safety, acknowledgement is obvious.
My horniness starts in my mind and will either motivate me to acheive an orgasm or serve as a short term distraction like a passing thought. The physical experience of arousal has nothing to do with emotion. It can be caused by feeling myself or being felt by another. Some parts of my body respond with arousal more intensly than others.
However, when my mind is stimulated I can also respond with arousal as when I was being photographed naked when I was 12.
I have no idea if this is helpful, but It is what I believe.