Ambien is not all that great, and their are older Med's better and with less side effects, the drugstores just do not stock them anymore...
Couple a Bloody Mary's , Melatonin, good cold medicine, DEA Scrip pad, 7 hour flight is not that bad, wait till you have a 12 hour plus flight...Never done one in the rear of the plane,
I would forget the Dr, most of them will not write it., so save you office call money.
Ambient does not always put me to sleep, they also have a time release formula, I have a scrip.
You also want to be alert clearing customs.
Just my thoughts, I would look for a couple of empty seats together, done that a few times in the old days, seats have not always laid flat.
Enjoy the trip, it is worth the ride,,