Who knows? I'm not sure what you're describing is OCD, but you gave only a brief description. It sounds like he gets unwanted thoughts which happens to all anxiety sufferers and also to those who suffer from depression. You can't have mental problems without unwanted thoughts. But as to what's happening now, it could be too many things for anyone to isolate. He should consult a physician and see if something is causing fatigue -- could be lots of things, like lack of exercise, poor eating habits, thyroid problems. blood sugar problems -- just a whole lot of things. But some people have nothing wrong with them either mentally or physically but just don't take well to sitting around. That's why a lot of folks have very active jobs and why lots of folks give up desk jobs, they just don't do well sitting around. As I say, no way to know, but if this isn't how he normally is then a good thorough physical is a first step. I know that both my wife and I are writers and both of us work in spurts, we can't sit and work for hours and hours as some are able to do. Maybe your bro is like this as well. Peace.