The problem with a 15+ hour flight is that you can sleep, which I have done, wake up, and find you still have 12+ hours of flight time left. So you get up and walk the cabin, or in my case, the house.  The clock by the bed showed 1:11 when I woke up.  In China, Ping told me shortly after we met, that November 11, the day in question, was known as bachelor's day.  It is because 11-11 looks like four single men standing alongside each other.  When I saw the time, the same thought popped into my head.

After walking the cabin you return to your seat.  You still have 12 hours to go.  But those powerful engines are pushing you toward home at greater than 550 mph unless you are fighting a headwind.  It is only in your little vacuum that you seem to be sitting still.  Time to sleep some more, you think.  You left Hong Kong in broad daylight, not long before lunch, and you need to start turning your body clock around.

So to sleep it is.