When I was little, I was deathly afraid of the dark. Part of the problem was that I had a vivid imagination. In my mind, darkness was not the absence of light. It was a house full of deformed creatures whose sole purpose was to harm me. 
When I was about 2 until I was 4 or 5, I slept on a trundle bed. Mara (who is 11 years older than I) slept a foot about me on a twin-sized bed. Although I was close to her, I couldn't sleep unless 1) she held my hand, and 2) I was covered neck to toe in a blanket, even if it was summer.
In my young mind, a blanket could somehow ward off the monsters that resided in the dark. Sometimes I'd need two blankets for extra protection.
As I got older, my fears diminished, but they were never completely gone. Then one day, when I was about 9 or 10, I somehow managed to convince Mom to let me read Dr. Jekyll and Mr. Hyde. The book was abridged, but it wasn't abridged enough! I read the book during the day but when night came I was a nervous wreck. The hideous creatures that lurked in the dark recesses of my bedroom were gone and in their place Mr. Hyde wandered, master of the shadows. The night after I finished the book I could not sleep. By now Mara had her own room and she was no longer there to hold my hand (even if she was there, I doubt I would have asked her to hold my hand because I was quite aware that other girls my age didn't hold their sister's hand before going to sleep). It was the middle of summer and quite humid, but I piled on the blankets, covering even my head.
I sweated a lot that night, partly from fear and partly from the heat emanating from the blankets I had covering me. I survived, but it took me about a year to subdue my fear of Mr. Hyde. I told myself I would never read Dr. Jekyll and Mr. Hyde again and I continued sleeping with a blanket every night, even during the summer.
Fast forward a couple years. I am taking a class, and guess what book I am required to read? That's right, Dr. Jekyll and Mr. Hyde. Not the abridged version, the whole thing. I was dreading it and I feared the return of nightmares. I was no longer afraid of the dark (okay, that is not entirely true. I can get squeamish when I'm downstairs alone at night). Surprisingly, I really enjoyed reading Dr. Jekyll and Mr. Hyde. But what I was very happy about was the fact that my fear did not increase, and that I didn't see Mr. Hyde lurking in the shadows at night. 
I discovered something else. I realized that sleeping with a blanket every night has become a habit. I still do it, even on the hottest summer nights. I also realized that my fear has changed. I am afraid that someone will grab my feet and drag me out of my bed. When my fear changed, I don't know. I think it must have been gradual, because I didn't notice it until it was upon me.  But guess what protects me and keeps it from happening? My blanket.