You know md80... really does have a point - and what he failed to mention is that on a 14hr flight, with a departure at midnight, 6 plus hours is spent lying on ones back or at worse sitting in a pax seat resting.
You must be one of those lucky few who can fall asleep on command and sleep well. Not all are so lucky and it can often occur that you fail to sleep well before the flight, and then get disturbed in the crew rest and get maybe 3 hours of actual, REM sleep (the only restorative sleep) "catnapping" while helpful does not always alleviate the tiredness one feels on ULR ops...
Do you really fly long haul??