Quite different topic though. JWP1938 was obviously of the opinion since the autopilot does it all both pilots could sleep all through cruise to be refreshed for landing. A real sleep is something different to napping. Napping was originally developed for a three man flight deck and is nowadays used as a bandaid on two man flight decks. There is a procedure to be followed and there are time limits for the rest, recovery period and distance to TOC as well as required calls from behind every couple minutes.
And then there is uncontrolled rest or sleep during flight which is a reality, doesn't care about any procedures, time limits or anything else. Usually caused by cumulative fatigue which is the real topic here. However sleeping isn't the only thing that can happen if you're fatigued. Fatigue impairs the immune system, leads to breakdown of any normal sleeping patterns and causes a breakdown in airmanship and decision making. It is something one can experience very easily if rostered to the limits of EU-OPS. We had that the last two summers and as a result at the end of the summer period sickness levels rose to 25% of the pilot force (the company doesn't accept fatigue, it is sickness in their eyes), crews were falling asleep randomly and there were some very close brushes with serious incidents, thank god nothing big ever happened, but a lot almost did.