Many of my friends say that they are afraid of the dark and they cannot sleep at night without keeping the lights on. In fact, we all are also aware of this somewhere when we were afraid to sleep alone in the dark, Specially when we watched a horror movie that night. 

The real problem starts when the fear starts to alter the truth of mind and our mind starts hallucinating many things. Then we start seeing the shadows, weird noises of moving doors and windows. we start to realize that there is a someone sleeping in our side and so on. 

With time this fear goes away and when you come out of this fear then you come to know your true nature. I laugh now remembering my experiences, But we all have faced this fear in our childhood. You can share your experience in the comments and tell how you worked on this fear.