@REI-AliciaS While I don't recommend doing drugs, I did have a doctor prescribe Xanax on my flight to England and another trip to Australia. I used to not be able to sleep on a plane. While England is only a 6 hour flight from here, it still helps.
On my Australia surfing trip, it was a 17 hour flight from San Fran to Sydney. Xanax saved me a lot from the awful jet lag. I slept a solid 8-10 hours in the middle seat on a 777.
All of the being said, I don't recommend taking it more than the flight. Xanax can be quite addictive. And don't even think about drinking. Alcohol plus Xanax equals respiratory distress or arrest.
An alternative is melatonin. It's not as effective, but a lot safer.
Regardless, talk to a doctor, PA, or NP before doing any of the above recommendations. Be smart, be safe, and rest well.