Indeed, the freezing IS the adrenaline. Your body pumps the adrenaline, yet your brain doesn't know what to do with it.
To get over something like this I suggest going to a gym somewhere and take up boxing. They will teach you how to punch, and in the long run you will get over that wall.
I used to be the same way when I was allot younger. Around 11, I got into a fight, but I froze up and completely got my butt handed to me. Well I didn't like this so I took up boxing, muay tai, and krav maga.
After that, any fight I got into I had three specific rules of engagement.
Is the person at a safe distance, and only mouthing off? If yes, then nothing needs to be done, your fine.
Is the person possibly going to harm me, and is moving closer? If Yes then get into a ready stance. Spread your legs slightly to get your balance and a proper platform for attacking.
Is the person now within arms reach, trying to "Bump Chests" as I like to call it, or just being agressive in general? If yes, swing first catching him off guard. Do as much damage as you possibly can. Run.
I know you weren't exactly talking about fighting in general. But what you did was perfectly fine in my book. It wasn't any of your business, he wasn't going to hurt you so you didn't need to interfere.
Take up boxing, even if you can't get classes go to any gym, find a person practicing and ask him to help you. Usually all of the people who do boxing LOVE to help newbies learn the sport, I know I do...