Power Sleep, by Cornell sleep researcher Dr. James Maas, transformed my idea of naps. I highly recommend the book. He recommends short "power naps" to quickly get in some rest. The key is to wake up before your body goes into a deep sleep cycle. For me, this means approx. 15-20 minute naps when needed. It truly is astounding how much this rejuvenates you. These naps were insanely helpful back when I was in college.
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I just wish naps were more accepted in the corporate world. When I have a startup again, I'd love to have a "nap" room for employees. Google has sleep pods: http://www.businessinsider.com/google-sleep-pods-2010-6