When I first started to play dayz, ran through some random village with like 10 zombies behind me. I screamed like hell! And when I shot a sniper that was 20 to my left side, I swear that my heart was doing 180 beats per minute.
Don't feel bad about it dude. I've killed 11 people as we speak and I think like this that it is either him/them or me and my friends, so keep up the killing!