I tend toward catastrophic thinking. There are probably many of us out there who do, and though experience should have taught us by now that the worst-case-scenario is not the most common scenario, we refuse to believe it until we're safely on the other side.
If we were rational creatures, then perhaps this could be constructive--preparation is key and all that--but, petals, I'm sorry. Humans are rarely rational and the worry and fear and projecting gets us farther and farther away from a centered place of well-being.
I don't have any advice or any way to stop the downward spiral. But I can say this, and I hope it's of some comfort--all that dooming your mind is doing? It's just entertaining itself. You don't have to get involved.