You may have had certain things happen in your life, certain emotionally charged situations, and they caused this anxiety to be learned to be formed. However you weren't born this way. This anxiety is a learned unconscious way of protecting you. It's something you have learned. Sometimes people take a while to learn things, and sometimes things can be learned in an instant. However sometimes at some point something significant happens that causes a heightened state of emotion, or a response in the body, and that response became instantly automatic, as a form of protection.

And that response is learned, so when your brain or your unconscious mind, recognizes some sort of pattern linked to that event, it's like it forms a part of you that responds as it had in the past as an attempt to protect you.

And it activates your fight or flight response. And this part doesn't want to hurt you, it wants to protect you. It wants to protect you from exactly the same thing. And it's like you can anticipate it, almost like you can predict it. It's like we already know it's going to be one of those events, and it's like the body is already geared up to protect us, because we are imagining, on some level at least, our worst case scenario.  We are always imagining, I say " Arnold Schwarzenegger" and I'm certain something comes to mind. We are always imagining, and the thing is our mind, our body doesn't understand the difference between imagination and something that is happening right now. It responds exactly the same. And through the act of our imagination we are constantly giving ourselves suggestions and those suggestions stick.
I'm not good enough, people don't like me, everyone judges me, I can't speak my mind,
When we imagine these things routinely they become automatic ways of thinking of feeling and being.

We get what we imagine. So when we imagine the best case scenarios we tend to generate that,  the opposite also applies.