Why are my sims depressed?

I had this happening to one of my sims a few weeks ago. I've never seen it before. I assumed it had something to do with his traits and the traits of others around him. But he'd be elated and then completely red and depressed in split second. His bar just rushed down. It only happened for a short time though and I don't remember how it stopped. He has the brooding trait and his wife is evil and mean spirited - but she was asleep and hadn't done anything to him recently.