My new Girlfriend tried something I never even thought of.?

We have been having intimate relations for a few months now. She is very comfortable with and loves to try things. One time she wanted me to lie prone while she stimulated my perineum and testicles orally. It was kind of making me self conscious, but she was kind of forceful about it and just kept doing it a lot. The all of a sudden in a short time my whole body was wracked in an extremely intense climax, without even touching the spots that normally make me do this. How is this possible? It never feels that intense from me touching it myself. Is this normal?