Yeah, for some reason OCD/ADD can act in weird ways to make a person have rather morbid thoughts. At least that's what I've heard, any refutation with backing evidence would be acceptable at this time.
I have ADD that causes me to overfocus on one thing, and thus I have a hard time changing what I am doing. I stopped taking medication for it five or six years ago. I also have something along the lines of OCD, but the symptoms go up and down in severity.
I also twitch and spasm, and I can't tell if it's voluntary or not.
I don't think I have any diseases, except maybe acid reflux.