How many times have you tried to fall asleep and struggled to get comfortable? How many times do you toss and turn until you start to get sleepy? You lay in bed surrounded by thoughts that preoccupy your subconscious and you desperately want to fall into a lull of slumber, yet it takes hours.
Have you ever considered it’s your body's way of protecting yourself? Maybe because somewhere in your closet, or the far side of your room, or even outside at the window, someone is watching you, waiting to strike. Maybe he is waiting for you to fall asleep so that way, he can attack you without you fighting back. However, the longer you are awake, the more impatient he grows and then leaves to find someone else.
This is purely theoretical of course, since there is virtually no proof, but this is something to think about the next time you are trying to fall asleep and you are riding the polished rails of thought.