Why Human Beings Normally Sleep at Night?

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.