Knock on wood.
I have very little control over my thoughts. Whenever I'm given the opportunity to think, I am bombarded with every horrible thing I could possibly think of. Often these are worst case scenario things (ex, something horrifically bad happening to me, a loved one, a pet, a child, the world, etc...).
Every time I have these thoughts I need to knock on wood. It started out as an occasional thing, but now it has become so frequent that it interferes with my daily life. Sometimes I feel compelled to knock on wood even when I haven't actually thought of anythign bad, almost as though I was cancelling out some "subconscious" thought.
Just before I go to sleep, when I have these kind of thoughts the most frequently, I have to reach over and knock on the wooden floor to cancel them out. But every time I do that, my body "wakes up" from the sudden movement and it takes a while to get tired again. This has caused me to stay up as late as 5 in the morning.
I have tried telling myself to break the cycle and stop knocking on wood, but I cannot let myself for fear that my knocking really does have some influence on whether or not these fantasies will come true. I know it's irrational, but my mind won't let em take the chance.
And by the way, as I was writing this I knocked on wood several times.