I fight for self-defense, and there've been times where they tried to attack my family members and I had to fight. In those fights, I was scared, not just for myself, but scared that others will get hurt as well.
Unfortunately, I've also been in my share of fights over stupid things, and getting angry over nothing in my younger days. There, I wasn't really scared. At that time, I viewed it like a normal fight that gets the adrenaline running and you get pumped over. I don't fight having those hormones controlling me now, I use them to aid me. That testosterone and adrenaline will make you perform better physically, but what about mentally? You need both, and from my experience, those fights, I would start off controlled, then go all crazy, punching, kicking, kneeing, throwing the guy on the ground, etc. That was probably due to my lack of experience in stressful situations (I was a teen way back then too, so give me a break) and I would just be an animal, no better than a monkey in the zoo.