This guy is a multi time world champ. In front of a packed arena he kicked major butt at last year's nattys. It has nothing to do with a mental initiated problem.
He has something medical that causes massive drain of energy with exertion, which, therefore, no amount of training can fix. And, of course, you can imagine what that is doing to him mentally.
This!
As TNT posted, someone more "in the know" posted a while back that it was not mono, and that it was something serious, of a serious nature. That's really about all most of us know.
It is most likely lingering effects from whatever illness he had (has). I seriously doubt it has anything to do with losing his drive, folding under pressure, others scouting his weaknesses, weight cutting, or any of the other BS that gets posted.