Anyone have an from exercise?

On a couple occasions during a vigerous work out cl- suprise! I noticed myself teetering on the edge of out of nowhere. I'm not thinking about remotely I'm getting my burn on. . .usually lower abs, hip flexers, quad burning exercises. Its awkward to be so arroused by nothing! I ure you its not my clothing or anything rubbing. When I used to go to clubs and dance all night to trance music this would happen too when my legs muscles are fatigued and burning, if I push through I get euphoric and very arroused. I've very rarely had this happen during though! What's going on? Would love to harness this feeling in bed- not at the gym, yuk! Any thought?. . . . .