h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

What am I scared of...well, it's not very cool to admit it, but I'm scared of the dark.
I don't mind the dark if I'm tucked up in bed . If I can't sleep for whatever reason and I make the mistake of looking around my bedroom, I can suddenly become four years old again, convinced there's a whole family of mutant monsters under my bed, all waiting to get me.
Recently, my boyfriend and I decided to watch the Shining. For the full cinema effect, we decided to switch the lights off. We lasted until the shot where the little boy is cycling on his tricycle down the endless corridors of the hotel. It really is a great sequence - so well filmed and full of suspense - but after he arrived at the door...well let's just say we had to switch the film off for a bit, and practically draw straws to see who was going to be the brave one to stand up, walk to the door and turn the light back on so we could continue watching the film.
The dark gets my imagination revved up and running through various awful possibilities....all of which are totally laughable when I'm back standing in the sane daylight. Why my imagination cannot always display the same vivid creativity about pleasant things, I do not know!

Most people find scientific explanations dissapointing but here goes anyway. The way we think is strongly influenced (note that I didn't say controlled) by our genes. We evolved from creatures that got regularly eaten by things in the dark. When the sun went down, our defences went up. One of those defences was to imagine what was there so you could be ready for it. Notice that you feel safe tucked away small in your bed. You can enhance the feeling by literally curling up. Safer yet curling up with another person.

If you want to imagine nice things when the lights go down I'd recommend that you get yourself evolved by some kind of cat. Cats seek the dark. They can't notice a dark space without checking it out. Cats find tasty things in the dark so their imaginations are likely pleasant in the dark.

I notice that you didn't make the connection about prehistory, humans being eaten at night, cats finding things to eat at night... Hmmm. I get scared after lights out - maybe a kitten isn't such a great idea...