Exercise and a break from the computer are both a good idea. I think you have to reflect on what happened but with some emotional distance. Remembering Thurber's observation that "humor is emotional chaos remembered in tranquility" you should write down your lessons learned once you can laugh about it (at least a little) so that you are not just re-opening wounds. Some amount of lateral drift (reading books, seeing folks you've neglected as your firm was failing, etc..) can also give you perspective on what to do differently next time. I had a painful failure about a decade ago and concluded "I am through with being an entrepreneur." After five years at a big company I realized that I had mis-assessed and that I couldn't help being an entrepreneur. Failing at a startup doesn't mean you should give up being an entrepreneur, but you should get some perspective on how to make "new mistakes" the next time out.

This reminds me of my college friend who spent much of his spare time climbing the outsides of campus buildings, smokestacks, et al..

Then one day he claimed to be afraid of heights, which made me laugh. "How can you be afraid of heights when you're constantly taking risks at high altitude?", I asked. His response was something like: "Oh, I'm afraid. But I can ignore that and keep going."