Activity

Not sleeping at all certainly damages the rhythm. But for me the current choice is between a chemically-mediated 8-9 hours from, say, 12am to 8am, or a natural 5-6 hours, from 2 or 3am to 8am. Both are similar in terms of the day night cycle, and not close to as bad as sleeping in to noon (and later and later) would be, I think.