I have personally witnessed the professor's hibernation for days at a time. The most amazing story of him sleeping for the better part of a week was recently busted when my brother admitted to slipping the prof a sip of water or a crust of bread during the "sleep."
I know for a fact that when Dai was at odds with the world, he never took a drink, used any dope - He just went to bed and stayed there until he felt the world was OK again. He did this his entire life. He was also not a diurnal creature but a completely nocturnal one. If you look at the the time stamps on my posts you will see that I inherited that quality.