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 am the exact opposite. I can conk out in a widebody jet but the domestic jets just feel too claustrophobic. I do tend to doze off here and there but on international flights I can get several hours at a time. The free booze helps as well.