I have flown many time to China and that is a 14-16 hour flight in Economy section. Get up and walk every 11/2-2 hours. Do not drink much acholhol on the flight drink water instead. Wear very comfortable clothes. Go to the back of the plane where the galley is to stretch and stand a while if the seatbelt sign is off. Get an aisle seat if possible or a window seat if you are planning to take the sleeping pill as suggested.