If you're one of those people who can fall asleep on a clothes line, its fine.
However, if, like me, you're one of those people who never, ever sleeps on planes, hates having smelly bastards elbows in your face, always gets off a plane with a broken neck and bird flu symptoms, and are generally irritable, it's absolutely horrendous.
Make sure you have an ipad, a neck pillow, some knock-out drops and don't drink booze unless you enjoy severe dehydration.