It's pretty normal TS. Usually you react in 3 ways, you run, you freeze or you fight. Fighting is more natural when you are angry. When you are caught off guard, most people freeze up. It may sound stupid, but it's survival instinct. You percieve a danger and you are trying to prevent that from happening by playing dead, so to speak. It worked for our ancestors, don't take it personally.
Same thing happened to me when I was younger. The thing is, you can break that mindset if you want. It's all about your state of mind. If you are scared of getting hurt, or thinking too much about what COULD happen, then you wont react simple as that. You just have to embrace the fact that it's either you or them. You have to embrace the fact that you probably will get hurt. You have to be willing. That's the nature of real violence. It's not pretty like the movies. It's chaos really. The more you embrace that fact, the easier it is to act. Going to a gym can help in part. Getting some good, hard sparring too. But in the end it's all about the mindset.
The important thing is you came out of it with your health. Don't sweat it.