Falling asleep on an airplane happens frequently.
There's something about the pressure or the altitude that gets you drowsy, regardless of how uncomfortable the seats can be.
However, you should try to avoid sleeping while landing (or taking off, if you're in a rush to doze).
The air pressure changes quickly in these stages of flight, and if you're not ready for it you could do damage to your eardrums.
If you're sleeping, you could be inhibiting your body's ability to acclimatise to new pressure.
A British pharmacist called Angela Chalmers told the Express:
A quick change in altitude affects the air pressure in the ear.
This leads to a vacuum in the Eustachian tubes which makes the ears feel blocked and sound dull.
Try not to sleep during takeoff and descent as you will not be swallowing as frequently and this can lead to blocked ears.
It's partly why people drink water and chew gum or boiled sweets while flying - the action of swallowing frequently clears the air.
So unless you can chew wine gums in your sleep, try to stay awake.