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.
Sometimes I can, other times I can’t. Same as in a bed.
But seriously did a lot of night time car trips when I was a kid. I think I was conditioned for car-colepsy. Oddest chair I fell asleep in was during a dental filling.