“Siesta” is a Spanish word that comes from the Latin phrase “hora sexton” -- or “sixth hour” six hours after dawn. That kind of afternoon nap was favored by Leonardo da Vinci. He slept two hours a night but took a 15-minute power nap every four hours. That’s only 4.5 hours a night. He must have had a relatively rare gene that allows brain restoration with short sleep -- and he had the good sense t…