Being able to sleep on overnight flights has lots to do with where you are seated and if you are flying charter or a "real" airline. Some things that work for us (not on a charter):

If you're lucky and there is extra space on the plane(don't hesitate to ask the staff about moving just after takeoff), you can stretch out a bit after the meal and truly sleep.

Lots of wine (freely available for the asking on a non- charter) helps to make you sleepy, just make sure you drink lots of water.

As far as pills, we have found that "allergy medicine" which is the same ingredient as sleep pills, "diphenhydramine HCL", an antihistimiane, works great, its an over the counter med, and will give you a good sleep without making you dopey the next day.It would be good to try it before you go to see how you react- everyone is different!

Good luck, Annabelle and Bill in Barrie