I used to have terrible trouble if I couldn't sleep in with smene else LOL. I watched this one film 'I, Madman' - which we had to turn off and couldn't sleep all night. It's like with most things, you become de-sensitized to it.
I never watch the excorcist, cos I wouldn't be able to sleep - and when I saw the grudge I had to leave the light on - but it's kind of part of the fun of getting scared.
My suggestion would be to watch a horror film, and then as I've done with many friends who get creeped out by them, we watch a rom-com or a Disney film after so we don't go to bed with the horror still fresh in our heads. Hope this helps