I've been afraid of the dark since I was 4. I never switch off my laptop, when I go to sleep at night I try to go to sleep before it goes into hibernation mode. Otherwise if I see the computer screen go black and my room goes dark I get a shudder down my spine.
It used to bother me back when I lived on a farm which was pretty desolate, but now that I live in the city the dark doesn't bother me anymore.
Perhaps its relates back to a feeling of a lack of physical safety in my case.