The most recent or near-recent Trains featured a full-page photo of a UP locomotive engineer with his feet dangling out of the cab and apparently fast asleep in a moving train. I didn’t know it was possible to sleep for more than a few minutes before the timer kicks the brakes on.
Anyway, if there’s a conductor in the cab, I suppose they could take turns sleeping as only one person really needs to be awake. That way, they are more alert when they awake.