First of all, I want you to feel comfortable as you read through. It is common knowledge that a large percentage of the people in the world are, in fact, afraid of the dark. This happens for many reasons and I will cover a few today.
1.) Fear. Fear is likely the number one reason why people are afraid of darkness. With mainstream media focusing on various entertainment strategies, homes with animals and other odd sounds noticeable when it's quiet, and many other examples are why fear is existent and in fact bothersome for some.
2.) Diet. Diet is another reason for some people as to why they are afraid of the dark. It can be that they ate shortly before going to bed and this active chemical breakdown going on inside the body can interfere with the calm meditation required for a restful night of sleep. Many will complain of nightmares when this happens.
3.) Nutrients. Did you know that your body will actually tell you when you have too much or too little of any of the many nutrients necessary during digestion? With the mass production of foods to increase people fed and profit we are no longer given all of such nutrients through markets and other food chains in adequate supply.
4.) Anxiety. Anxiety can be of everyday life stress, changes with medications, and side effect of most health issues. If you know about anxiety then you already understand how this can be manifested into fears.
Tips: It is NOT your fault! Nothing is wrong with you. The best way to overcome this fear is to accept yourself. Repeat over three times, "Although I am afraid of the dark, I completely and lovingly accept myself." No you do not have to say this out loud. Be sure to say it in your head three times in a row each and every time you think of fear, darkness, or anything relating. As soon as the negative thought is recognized say this three times. When you walk outside in the dark say it three times. Before your imagination comes up with a new story or idea about the dark, you got it! Say it three times. If three is not enough you can increase it but work on reducing the number of times it needs to be said later.
Why the dark? I'm sure you are wondering of all things I am afraid of why the dark? The most likely answer to this has to do with our minds needing something to focus on. When there is no focus everything becomes unknown. Unknown enhances our imagination. I do think this is why meditation during daylight is healthy for all! Especially for those who are bored, with writers block, inventing, or even just figuring life out! Silent and non-visual meditation helps to stimulate the mind. If the mind is stimulated during the day it can help with the ease to sleep through the night.
Other Articles of Interest:
http://0-www.pbs.org.librus.hccs.edu/wgbh/nova/blogs/physics/2012/04/whos-afraid-of-the-dark-alternatives-to-dark-energy/
http://www.las.illinois.edu/alumni/magazine/articles/2013/dark/
http://www.chop.edu/healthtips/fear-of-the-dark.html