I am much older now, but when I was younger, I was extremely agressive myself. I had no idea what I was doing when I would get into a fight, but I would get in many. I lost a lot too, lol.
Anyway, everyone here pretty much hit the nail on the head.
You need to find out what is important and "worth fighting for".
When that phrase is said, what does it mean to you?
To me, it means, what is worth getting physically harmed for? What is worth physically harming another? Is it worth going to jail over? Is it worth the consequences and worry that your family may encounter if something happens to you...or, vice versa......is it worth possibly ruining another family's well-being?
If some guy gets drunk and is mouthing off and you fight him and hurt him bad.....was that really worth it? Even if he attacks you and you are trained, you should be able to use (at first) the minimal force possible to defuse the situation. And what I mean by that, is by putting him in some sort of hold or something until he calms down. If he gets up after that, well, maybe you have to take it to the next level, but you would need to be calm and "level-headed" enough to realize when enough is enough.
Also, remember this: You are training to fight! You are learning things that a normal everyday-joe off of the streets does not know. And, at the risk of exposing my geekeness, a quote from Spiderman is, "With great power, comes great responsibility".
Imagine yourself standing in front of a judge or a jury and being asked why you just didn't walk away.....
Imagine yourself standing in front of a judge or jury and being asked why you took it to the level that you took it to. They are going to find out that you are trained and (usually) you are trained to know when you need to really hurt someone and when it is better to defuse the situation with the least amount of force possible.
I witnessed a situation in a bar where some jerk was drunk and causing a scene and he put his hands on someone that was trained. The person that was trained calmly grabbed the guy's hand and put the guy into a "chuno-lock" (I do not know if I spelled that correctly). While the trained fighter had the drunk in the lock, he calmly asked him, "do you really want to do this? Because I don't." and after that, the drunk guy realized that it was probably not a good idea to continue the fight, and it was over. That is what should be done when you are trained. The trained person could have easily snapped the guys elbow or popped his shoulder out of place....but why? Why do that when you can just end it like that?
Sorry, I will stop ranting now. But you really should seek medical advice. It will help!! Good luck...and keep your head!!