An Unhealthy Overactive Imagination?

I do this thing sometimes in my head. It's completely unhealthy and not the least bit rational. It's what you'd probably call "worst case scenario" thinking really. Here's how this goes down: So I'm in a cave the other day. We're crawling around in really tiny spaces, getting super muddy and I start to think: What if there's an earthquake and we get trapped? What if we run out of air down here and suffocate?! This is all despite the fact that, A. We live in Colorado and there aren't friggin earthquakes and B. We really weren't that far underground to run out of air... I mean, you could see sunlight most of the time. That's what I'm talking about. Or I'll be in a movie theater and start to think: If I was a terrorist, I'd totally infect the arm rests of a movie theater because it would spread really quick. How come they haven't thought of that one yet? What? Who thinks stuff like that?

Don't judge. Have you ever wondered how you would react if someone you loved died? You begin to play the whole scene out in your head; the phone call to your desk at work, how you would react and how you would be devastated and tragic at the funeral. You've done it. Don't lie. So why do we do this imagining of horrific things? Why when I'm in a crowded room do I think about what would happen if there were a fire? Or sudden volcano (I hate those sudden volcanoes)? I think it's because we want to mentally prepare ourselves for the horrific. I mean, if we never think about stuff like that, how are we going to be the hero in that situation? How can you save the bus full of nuns and children from rolling off the cliff if you never imagined how to do it in the first place?! You'd be totally unprepared! So see... I'm not irrational when I'm thinking of stuff like: What if I turn on the tapwater and nothing but spiders pours out? I'm prepared.