Thanks for the wonderful trip report, tfung! As for falling asleep prior to takeoff, I recall reading that it was due to a lack of oxygen. Not enough to actually suffocate anyone, but enough to cause you to feel sleepy. After pushback but before takeoff, the aircraft is just taxiing along pretty slowly, and the blowers are switched off. After takeoff, air is forced into the cabin by the sheer speed of the plane.
Perhaps someone familiar with civil aviation tech can say whether I'm right.