Simple but effective Air Travel Advisory –
It is not smart to sleep during take-off or landing on any aircraft, especially Long Haul air travel.
As you are in a pressurized container your ears need to adjust to the changes in pressure in the cabin.
In order to do this you need to be awake to unblock the vacuum in your Eustachian tube.
Yawning or swallowing will help along with gum chewing, sucking hard candy or drinking water.
Alternatively, pinch your nose & blow (gently) to relive pressure in ears & ear popping.