20 hour flights suck a lot, however, I'm not sure if 20h straight is any worse than 2*10h + a few extra hours in an airport.
I can walk around, find something to eat or read, people watch. Plug in a laptop and sit at a table that's reasonably comfortable to work on. Relocate somewhere quieter, or more interesting. See if I can find bathrooms that aren't slammed. Get my steps in / some exercise.