According to MedlinePlus, falling asleep during landing or takeoff could cause serious damage to your ears. It all has to do with the rapid changes in air pressure in the cabin.
If you’re awake, a natural response to alleviate pressure on your eardrums during takeoff and landing is to “pop” them, to maintain a pressure equilibrium. If you’re sleeping on a plane, you can’t actively work to relax those muscles and release the tension, so you can become susceptible to dizziness, ear infections, eardrum damage, hearing loss and nose bleeds.
“A quick change in altitude affects the air pressure in the ear,” says Angel Chalmers, a British pharmacist, via Express. “This leads to a vacuum in the Eustachian tubes which makes the ears feel blocked and sound dull.”
Keep those Eustachian tubes clear and keep those eyes open for at least another few minutes. Crack open that book you just bought in the terminal.
Source: rd.com