I can't sleep alone in the dark. My dog sleeps with me. I'm an adult and I'm terrified something can come out of my closet or somewhere else. I don't sleep or sit next to/with my back to doors and only started sleeping "alone" in my bedroom once I repositioned my bed.

This is gradually getting better. Years ago I wouldn't sleep by myself, with or without the dog and would leave a light on. If someone turned it off I'd instantaneously wake up, no matter how deep was my sleep, really.

I too suggest some controlled exposure. Can you trust someone to help you with this?

edit: oh my, this thread made me remember of so many stuff. When I was a teenager I used to believe my bedroom was haunted. I knew it wasn't, but it was an intrusive thought. I wouldn't sleep in in even in the middle of the day. I gradually started forcing myself to take naps there during the day by reading a book until I get sleepy. Then I tried going over the night and stayed the whole night up many times. I was simply unable to fall asleep before the sunrise.

Even now, I know I only sleep on my stomach with my head under the pillow when I'm really relaxed. I don't sleep in that position during the night in my bedroom... but will gradually shift to it as it gets closer to sunrise.