We're all there with ya. Ever since my roommate went home for the summer, that damned preview for "The Strangers" keeps coming on, and it has been freaking me out. Things are get really different when you're used to having people around and then they stop.
It's actually part of my fascination with deserted places. You notice how a place that is normally full of people is instantly creepy when there aren't any people in it anymore? It doesn't matter how fun or festive it looks, that place becomes creepy. It's almost as if there is some kind of force lurking just outside of our perception that is kept out by the comfort and good will of people who come together, but when those people are all gone there is nothing to keep it out anymore and it fills up the empty space.
Or it could just be that human beings survived this long because we banded together against nature and the elements, so the instinctive uneasiness of being alone is still deeply ingrained into our psyches.
Some nights when I am alone in my apartment, I am convinced that someone else is here, so I hide under the covers. You are definitely not the only person to have weird night-stuff.
Yikes.