You should tell your wife. It might be hard for her to properly understand, because she doesn't experience it, but she cares about you, and she knows you probably better than anyone else. So, she might know what helps you , or what not to say to you when you get down.

Being really, really down does hurt. But, it's not going to last forever. I always have to remind myself of that when I'm down- that eventually it will end.