What was/is your most irrational fear, than you know its completely impossible, but yet you can't help to think that it could happen?

When I was younger, I lived in a house that had train tracks running behind it.

Keep in mind I was very paranoid as a kid and was deathly afraid of many a thing, trains didn't get an exception.

My irrational fear was that one of these days that cursed train is bound to come off the rails and head straight towards my house, crashing right through it as we slept, and there wasn't a damn thing we could do about it.

Of course on I realize that this just isn't a possibility(or else I hope not, don't tell me if it is...please), but I can't help to feel a little unsettled when I hear or come across a passing train.