Discipline Equals Freedom Field Manual by Jocko Willink ( PDFDrive.com )

POWER NAPS
Power naps. They are real. If you are feeling tired
they can be a lifesaver. And if you are feeling tired
due to lack of sleep, they can be very powerful. I
have a technique for power naps that is a combination
of two things I learned.
The first was in high school. My anatomy and
physiology teacher was a high-energy, passionate
teacher. But if you went into his classroom during
lunch, you would find him sitting in a chair with his
feet elevated on the lab tables, sleeping. He did it
just about every day. One day I asked him about it;
he said his goal was to elevate his feet above his
heart and sleep for ten to fifteen minutes before he
ate his lunch. He said the nap gave him energy.
Elevating his feet above his heart took the strain
off the circulatory system in his lower body and
helped move some of the blood that might have pooled
in his feet and legs. I began to try it occasionally
and it certainly felt good.
But I really noticed it when I got to BUD/S, the
basic SEAL training course. Obviously, we were
operating in a fairly sleep-deprived environment
there on an almost daily basis and the schedule was
very tight, going from evolution to evolution
throughout the day, on a strict timeline. But there
were some holes in the schedule, usually ten to
fifteen minutes a couple of times a day for us to
prepare for our next evolution and use the bathroom.