Flew from Chicago to Hong Kong for years (14-15 hours per head/tail winds). Could be brutal. For flights over 6 hours here is what I recommend:
1- you need to get up and move every 4-6 hours and keep your blood flowing (helps keep you from feeling like total crap when you land)
2- narcotics and sleep aids were a NO GO for me, but was able to sleep with eye coverings and ear buds with 'white noise' playing. (side note: if you use any 'sound maker or fan' when you sleep at home, record it and put it on continuous loop, it helps)
3- compression socks, over the calf/to the knee help with circulation, helping when you land
4- quit being cheap and get Preferred Econ at least
5- bring $5/$10 starbucks gift cards on the plane and give to the flight attendants in your area, amazing what that will get you on a LONG flight.
I regularly fly now from Atl to Amsterdam and these still work quite well.
We fly to Tokyo in July, from MSP, it's about 12/13 hours, so I plan to carry out all 5 of these! Best of luck and enjoy the flight.