Because after being in a higher altitude, your senses are use to being in that lesser amount of gravity, and so when it decends, the plane, the gravity, and your sense, change constintly, making it hard to adjust at first. but chewing gum and useing really good headphones can help. i think :p
i don't know exactly why but chewing gum helps a lot. and swallowing really hard helps to because it makes them pop. haha i have lot's of expierience with flying so deffinetly try chewing gum
I remember, before jet planes were virtually universal here in Australia, the hostesses would hand out sweetmeats for the passengers to chew.
It's caused by the pressure change cause of the drop in elevation, as she said chew gum that has always helped me :)