Fear of the Dark

This is a thought that I have had before. If you came for a monster story or a tall tale, turn back.
There is this one feeling, I can guarantee you have felt it, or even something similar to it. However, I have had it multiple times, and I cannot explain it. You just cannot fall asleep, and there is no particular reason.
Then your air conditioner shuts off, most likely because it was getting too cold. Now you are left in the dark. That is when you get the feeling. The way that the dead silence has its own distinct sort of clamor, or even, well, a noise. It just wrenches at your brain for what seems like forever... but then, it heats up a little and your AC kicks in once again. It provides a sort of comforting white noise. That's when that... feeling... kicks in...
It is pitch black in your room, the only light is the moon shining through your window. However it is not enough light to see. The thing is, as soon as you shut your eyes, you feel as if there is something staring you down. It is waiting for you to peek out. Therefore, you do not open your eyes, even though there isn't anything there.
Why are we afraid of the dark though?
Why do we get the feeling that we are being watched?
You would think that being able to hear everything around you would be calming. Rather, it is unsettling. It seems like an irrational fear, but it also seems instinctual for humans to fear the dark. And in case you didn't know, most instinctual things, fears included, are for a reason.
So, explain what lurked... or lurks... in the dark that gave us this strange fear... 
Category:Beings
Category:Theory
Category:Micropasta