Orgasmic Spasms

This past weekend I decided I would attempt to have an orgasm from playing only with my nipples. I have always enjoyed stimulating my nipples during a masturbation session, and this night was no different. As the session I had a full erection,but, I resisted touching it. this went on for a few minutes and then it happened. My back arched, and I felt a wave of rhythmic spasms throughout my whole body, then my body relaxed. Not sure of what just happened I continued to play with my nipples. A minute or so later it happened again, I kept going and the spasms kept coming wave after wave, the longer I rubbed my nipples the more waves of pleasure I had.
I later discovered I did not need and erection to enjoy the spasms. I continued this for about an half hour,then I stopped, got an erection and masturbated to orgasm. The following night I did it again, same results. I really like this new discovery. I can not find any information about this.