Why mental workers keen on working into deep night?
At night, sun goes beneath the horizon -> water and nutrition in human body concentrate at feet -> nerves on feet relaxed -> muscles of feet relaxed -> heart relaxed -> brain calm down.
Q.E.D.
Then when shall we waken?
As soon as the water and nutrition are accumulated sufficiently to reach the head.
Why Human Beings Normally Sleep at Night?
原文：http://www.cnblogs.com/ybing81/p/4222281.html