Fear of the dark is instinctive. It's a natural protective mechanism for any animal whose senses are optimised for daylight. We are not at the top of the food chain because of our physical prowess, but because of our brains. When we are stripped of our daylight optimised senses, most of the advantage our big brains give us, is removed as well. Under those conditions, we are replaced at the top of the food chain by predators who have superior physical attributes and who are night optimised. It is our natural instinct to fear these conditions. That we live somewhere that most of those predators no longer inhabit, is irrelevant, because our instincts are genetically programmed. We can overcome them, take control and master the impulses, but it takes regular exposure to those conditions to desensitise. Equally, a lack of exposure to those conditions can make you hyper-sensitive. It's all natural, good and the way things should be. You just have to train your brain by rationalising your situation and not let it get trained in the wrong direction by succumbing to irrational thoughts and paranoia.