I have low orexin (but fortunately not full-blown narcolepsy, like my sibling). It basically means that I fall asleep in any airline cabin the instant the safety briefing ends, and wake up when the wheels touch pavement. If I don't recline, and wedge my head in place somehow, I always wake up with severe neck pain, because my head lolls into uncomfortable positions.

Airline flying is simply too boring for my brain to be able to stay awake for it.