joanek,

Excellent diagnosis. The issue here is a pressure imbalance between the sinus or innner ear and the external environment.

As a plane descends the ambient pressure increases. Imagine your sinus or inner ear as a balloon, as external pressure increases on the relatively lower pressure air of the balloon the balloon shrinks. (you've seen your potato chip bag expand as your plane climbs, right?) Inside your head, the lining of the sinus is the balloon. Effectively, that lining is attempting to shrink, pulling away from the skull. That's why it hurts.

How to fix this? Generally if everything is working correctly, the human body will equalize the pressure on its own. However, if you're congested or your eustachian tube is small or clogged it's going to need some assistance. One method is called val salva. To do this inhale a breath, pinch your nose, close your mouth and do as if you are breathing out with slight, gentle force, but do not exhale. This will force air into your sinus and the inner ear. Don't over do it. Just a modest push is all that's needed. You'll feel your ears push out a bit and your cheeks should blow up a bit also. If it's your eustachian tubes, tilting the head from side to side while performing the val salva will help to stretch the tubes out. Remember...val salva.