You might be surprised. Many soldiers have stated they experienced a feeling of elation after killing the enemy. They might feel bad when they get a chance to reflect upon it later but in the immediate aftermath? Often it's joy. The killed the people who were trying to kill them, they won, and they survived. Happy times.
I cannot rule out that possibility, not this side of the actual experience. I can extrapolate from past experience, such as the incident I mentioned earlier. I was happy and proud that I had accomplished my goal (stopping the original attacker), without paying the price of my life, or even any bloodshed; I also, in an overlapping interval, got the shakes.
Here's a hot take: humans vary.
I've known humans who delight in squashing spiders. I've known humans who would go to the effort of capturing a spider (with paper or some such) and carrying it to the door, to remove it without harming it. I've known humans who did the former at one age, and the latter at another age.
Some humans feel joy after killing, in certain circumstances. That doesn't mean all humans, nor all circumstances. General Patton, on at least one occasion, expressed joyful responses, on seeing the carnage of a battlefield, and his emotional responses were notably different than the emotional responses of several of his fellow humans in the immediate area (and in the same army).
"The right wing, where I stood, was exposed to and received all the enemy's fire... I heard the bullets whistle, and, believe me, there is something charming in the sound." - George Washington, in a letter to his brother, 1754. Perhaps humans such as Washington, and humans such as Patton, are a minority; and when their particular response becomes situationally useful, those humans rise to the top, much as Rudolph rose to the top *only when Christmas Eve was foggy*. Under other circumstances, they might not. I find the whistle of a bullet charming, largely insofar as it means that particular bullet *didn't hit me*. I'm glad that my species includes both me and Washington.