I only have a theory, but I think, in general, positive emotions (those that express good things, in general) result in more positive health, and negative emotions (those that express bad things, in general) result in more negative health. That doesn't mean that happiness cures everything, but I think it raises one's chances. Now, sometimes we need negative emotions, like grief, but we have to express it to release it, and that helps us be healthy. That can make a "negative" emotion a positive one, in some ways. Still, too much of this pain will hurt us, even if it's not under our control.

It's just a theory. I have no medical degree.