My wife and I have just returned from Siam Reap, via Hanoi. The journey including a 5 hour layover at Hanoi, took about 21 hours.

i find these journeys with late night layovers, absolutely exhausting even though we flew business class. How do regular travellers deal with these journeys?

I know there are a number of threads in the TravelBuzz forum that deal with jetlag and related effects of long-distance travel. Frankly, I think some people just cope with it more easily than others. These days it's not just the jetlag that bothers me, but the physical effects of sitting in a cramped area for hours on end. (I have chronic back, hip and shoulder pain.)

That said, I find that business or first class travel certainly alleviates some of the pain, though it's not feasible for everyone all of the time.

I try to start adjusting my body clock a few days before an east-bound flight, particularly a red eye, in hopes that I can take a sleeping pill and get a few hours of sleep on the plane. If it's a west-bound flight from the US to Asia, for example, I'll pull an all nighter in hopes that a sleeping pill will work on a midday departure. (I also have chronic insomnia, so even Ambien is not a guaranteed solution for me.)

If I'm stuck in coach, I've bought one of those foot slings, and sleep pillows/head rests to make it easier to doze if I'm unable to stretch out across a few seats. When I'm not sleeping, I'm frequently getting up to walk around on the plane, and to stretch if there's a spot where I can do it.

Planning for a slow day on the day of arrival helps.