Anxiety Disorder:

Long ago, when I lived at home with my parents, my father contracted a severe anxiety disorder. Verifiable, psychiatric level. He obsessively turned off the light in my room when I left it, even if I was gone for just a few moments. I explained to him with calm, reasoned logic how that light could not possibly require more than a few extra cents to simply leave it it on. But there was no persuading him.

Years later, I've came down with the same affliction. There's something about being responsible for the electricity bill that makes you succumb to neurosis.