Little late to help you tonight, but here's something that's helped me a few times:
When I've just got done watching something that I shouldn't have been watching late at night, something about all the scary things in the world that might kill me without warning... let's use insects for example... I realize that it might give me nightmares. And then: I inflate it.
I think about my room getting swarmed with the thing (say, bees or ants). Not a regular swarm, but a floor-to-ceiling, spilling-out-into-the-hallway swarm. And then I think about them being bigger, huge, like something from a bad sci-fi movie.
And when I think about the absurdity of being attacked by giant insects in my room, I can laugh it off and stop worrying about it anymore. Move on and think about other things.
Not sure how well this would work under a certain age, before you gain some perspective about the likelihood of certain things happening. Or, indeed, for certain personality types who might have an easier time accepting that outlandish things could actually happen. But it's worked for me, and maybe at some point it'll help you too.
ETA: If it's cute, fuzzy things you want, nothing beats a little trip to The Daily Squee: http://squee.icanhascheezburger.com/
