Crew Boredom not Fatigue?
From the latest reports, seems the crew had plenty of time for adequate rest between duty shifts. Not sure you can really regulate how they spent that time.
I can image a warm sun, good weather, and perfectly controlled temperature would help ease a lot of people into a nap! Always admired how the long haul crews remain alert during those endless hours of flight.
People vary greatly in their susceptibility to a lack of stimulation. Some people drop off to sleep easily, others remain alert and have difficulty going to sleep even when its time to do so.
Seems the challenge is to develop a system that gives the right amount of stimulation to keep you alert but not in itself cause fatigue. This is no easy task.
I also wonder if the military has any helpful tactics to deal with fatigue on their very long range missions.
On a side note, I have seen many doctors go without sleep for 24 hours and still be a much better doctor than some well rested type of lesser ability and skill. Have also seen doctors (usually the assistant surgeon) go to sleep in surgery even standing up due to extreme fatigue. You certainly don't won't that situation in the cockpit.