I can fall asleep almost anywhere. I routinely fall asleep in the break room at work. Once, I was helping a friend fix his car, and I fell asleep on his garage floor when he went inside to get water.
But in a hot metal tube tearing through the sky, with my neck all kinked? Get out of here, man.
I once read somewhere that it’s something to do with the altitude or the cabin air pressure that make people feel sleepy.
Personally. I can’t do it and I find it very uncomfortable even trying to get to sleep on those long journeys. Even if I do fall asleep, hoping to paas the time and it ends up not being long and time has never passed.