We’ve all enjoyed a nap on Metro-North. The swaying action seems to induce a nodding-off, especially on the way home after a long day in the city. But it’s sleeping comfortably during long distance travel that seems like the holy grail for travelers. On overnight flights to Europe we’re envious of those business class folks with their lie-flat seats. And on Amtrak, even the comfiest reclining coach seat can’t compare with the beds in the sleeper — be it a one-person roomette or a deluxe bedroom.