Back in the day when I flew/travelled I found if I kept busy during a flight it helped.
Ordering drinks seemed to work.
I did two very long haul flights to Hong Kong and you feel very drained at the end of it - lots of drinks in the first half of the flight, sleep on second half, then go straight out for the evening, meal and drinks and finally to bed. You wake up refreshed (well I did) and ready to start work (it wasn't a holiday).
I have flown to the USA twice and that isn't that bad for flight duration.
I also flew to Brazil and you first have to fly to France as there is no direct flight to Brazil from the UK (or there wasn't then). We flew on a Varig Airlines aircraft there was an interesting article in one of the in-flight magazines in the back of the seats - it was all about a Varig Airlines crash, with some gruesome pictures in the article. I guess they never checked the in-flight magazines