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.
Diphenhydramine, melatonin, neck pillow, and EYE MASK. Critical to block out light. Bonus for noise cancwlli headphones playing noise.