Hmm. . . I certainly can't provide any 'answers' for you, but maybe I can suggest some ideas to consider. I, too, have had bouts of real lethargy and extreme exhaustion, though I hardly have the ultra resume that you do. Overtraining, which you have already mentioned. If I am being lazy and not training, I can sneak by with less.
Sleep is the best recovery-booster there is.
If you aren't taking in enough calories overall, you could see symptoms like you describe. In our diet-crazy culture, we are sometimes subsconsciously guilty when eating good quantities of good food. Not a pleasant experience. Those are my best guesses, hope they help. Then they try to say that the two are related.