Columnist Jonah Lehrer thinks about insomnia:
[W]henever we try not to think about something that something gets trapped in the mind, stuck in the recursive loop of self-consciousness. Our attempt at repression turns into an odd fixation.
This human frailty has profound consequences. Dan Wegner, a psychologist at Harvard, refers to the failure as an "ironic" mental process. Whenever we establish a mental goal — such as trying not to think about white bears, or sex, or a stressful event — the goal is accompanied by an inevitable follow-up thought, as the brain checks to see if we're making progress. The end result, of course, is that we obsess over the one thing we're trying to avoid.
I will be thinking about that tonight, I'm sure.