In my case it was just from the excitement and adrenaline from the fights and not the outcomes as 3 of my fights were broken up fairly quickly. I don't know for certain about my friend's reaction, but I'm pretty sure it was the same, adrenaline etc
It's a flight or fight response. Although we're one of less than 5 species, which enjoys sex for way more, than just procreation, we're still hardwired to enter survival/prepare to procreate mode upon impending doom. That's the same reason why people who're executed experience the same reaction, and you allude this with the adrenaline rush.
A key problem with some very horny men and lesbian/bisexual women, that their laser focus on combining fight with sexual pleasure (and this a sexual fetish after all) leads them to the erroneous belief, the fighting women have the hots for each other, or the impulse is unbreakable and needs to be satisfied with the first person they come across.
In my strictly personal opinion, that's behind this question too, in which case it would be a not so subtle form of fishing for ways to convince women to fight for them without making the effort of compensating them for it.