I'm resurrecting this four-year-old thread because Pat made a good guess, and it might be interesting or even valuable to future searchers of this website to bring closure to this thread. It turns out I do have an anxiety disorder, and I've had it all my life. I wasn't conscious of it until my diagnosis, but looking back, it explains everything, including the ostensible "overtraining" I was complaining about in this thread.

I collapsed two weeks after the date I began this thread. I was in bed for a week, barely able to move, my physical weakness was so intense. For the next half year after that I experienced recurring panic attacks and debilitating episodes of anxiety. It was a living hell. The doctors checked everything, again, and found nothing. I myself did exhaustive web searches and came up with numerous potential diagnoses: chronic fatigue syndrome, lyme disease, hemochromatosis, etc. But nothing was conclusive. I started to think it was all in my head, and my GP agreed that that might be a possibility, so to speak. He started me on an antidepressant, and that basically did the trick.

Drugs. Yep, drugs. So I took the SSRI for a year, and felt so much better that eventually I stopped taking it. The next two years I was basically fine, and I figured I'd recovered. But I was fooling myself. This past fall I started to stop feeling fine, and at first I was confounded. Hadn't I "gotten over the hump"? When the physiological symptoms got debilitating I went back to the doc, and he said a simplistic explanation might be that my serotonin and dopamine levels had probably been fine for a year or two after stopping the medication, but were now depleted again. So I'm back on a low-dose of an SSRI, and am feeling better.

So, no, I did not overtrain. Instead, the stress of the fallout of 2008, when my wife and I thought we might lose our jobs and our house, exacerbated my underlying but heretofore manageable anxiety. The combination of clinical anxiety and financial stress turned out to be a killer. Well, almost. Knowing what the problem was was half the battle, and getting the right help was the other half.

All I can say is: what a relief it has been.