In my "bad old days" I had some fights. Quite a lot, by civilized standards. I feel sort of stupid talking about this - I don't want to sound like I'm strutting around here being all badass, because I'm a Christian and I really try not to fight nowadays.
I had a head injury (frontal lobe) when I was 16, and during the first ten years thereafter had very serious anger management issues. (My family agrees that I woke up with a different personality than I'd had.) (There are still moments when I have troubles.) After the head trauma, I began experiencing "berserk" moments during hostile situations.
There were several fights when I would get into a weird "berserk" state. My voice changed (drastically), and I was unbelievably full of adrenaline. I felt stronger, and I was clearly scarier. It freaked my friends out, and concerned them (even some guys who were more into fighting than I was). My thinking sort of "tunnelled out" to where my only focus was smashing and hurting. I did not experience loss of memory - just a sharpening of focus on exactly what I was doing and nothing more.
During these moments nothing that happened to me seemed to hurt, and frankly I don't think I wound up as injured afterward as I should have in several instances. I would not stop fighting when I should have stopped fighting. In one instance three of my friends had to beat me up to get me to stop beating this guy's head against a pole (he'd kicked me in the yarbles to show off his kung fu prowess). My friends had sort of started the fight (they were more aggro than I ever have been), and they were really freaked out by the way I'd gotten.
It did not happen in every fight I was in, and it happened on several occasions where I wound up not fighting (in which case I started shaking pretty dramatically and uncontrollably, and felt like I needed to drink a whole lot of liquor quickly so I didn't hurt anything). It probably happened a couple of times a year until I was about 28. It hasn't happened in a long time, and I really try not to go there. I'm pretty sure I could still go back into this weird state if I were in a fight. I try really really hard not to get in fights.
Anyway, like I said, I don't want to sound like I'm trying to be a tough guy. I'm so glad that I have myself more under control now, and I pray I never lose it again.