probably becasue I did so much of it as a flight attendant. I flew only trans-Atlantic and trans-Pac flights - and we did get a sleep break on the trip - but sleeping for an hour or two instead 7-8 hours only made it 10 times worse for me.... I was actually much better if did double doses of caffeine and just stayed awake- but that was so hard on the body becasue every 3 day trip you'd lose a whole night of sleep.
Now can't even think about skipping sleep. So I don't understand the "combat nap" theory becasue it only made me groggy, lethargic and in general much worse.