Two or three of those I've seen fall are exact fits for "I went from working hundred hour weeks to quasi-retirement", and they did not treat their burnout with the respect and healing I feel it requires. When they took away the overwork, the unhealed burnout smoldered and eventually caught fire and burned them, weeks or months later.
Is this what took down Hsieh? I haven't a clue, and it's unlikely I'll ever know, and I certainly don't intend to bother anyone to learn more about his circumstance. His friends are having a bad enough time as it is and I empathize too strongly to press for more knowledge.
Is Hsieh's story familiar from personal experience? Yes, absolutely. In the couple of press articles I've read, and a couple of quotes from a letter from a friend to him in one of them, there is certainly material enough to remind me of others I've known who worked themselves to the bone, sold it all and rested, and then a while later (a few months to a couple years) self-destructed.