To preface this, I'm 16, from England, and closeted transgender, if that means anything in my situation. I hope this is an acceptable use of this Subreddit? It's staring to bother me. 

For most of my life, I've been having strange thoughts, but I've only really come to realise it in the last few months.

Essentially, whenever I get a piece of new stimuli, for example, I hear a car approaching, I immediately think of a terrible, yet incredibly unlikely scenario. Instead of thinking "thats a car driving by," what goes through my head is "that car is going to stop, someone's gonna climb out and throw you in the back."

The thing that gets me, is that I know it's not gonna happen, I know how incredibly unlikely something like that is, but it bothers me. I had that thought when I was walking to the shop, and for the whole way back, I was on edge. I ended up running home.

Another case, a few hours ago, I heard a cable slip down off of a desk, and my immediate thought was "someone in the house coming to murder you" rather then "random noise, nothing to worry about" and once again, ended up panicking. 

I'm always considering the worst case, most irrational scenario in a given situation, and I end up starting to panic. Is this normal? Is there a word for this?

Responses are much appreciated; thanks in advance.