I have a question about sinus infections and a traveling on a airplane.  
I'm asking this question because of an incident I had about a year ago when
I flew and had a sinus infection.  I'm not a medical professional so some
of my descriptions may not be medically precise but I'm trying to describe
this as accurately as possible.  I was flying a commercial flight
(Southwest I believe).  Take off was fine, and the flight was fine, but my
problem began as the flight began its decent in to Phoenix Sky Harbor.  For
some reason, the pressure did not change in my right ear (or did not change
as fast).  I kept waiting for the regular pop but never came.  Instead it
became painful.  As the plane descended more, it became more and more
painful.  A short time after the plane landed the pressure seemed to
equalize and the pain gradually subsided.

This was a very painful experience that I don't really care to repeat.  I
have a sinus infection and I'm flying tomorrow.  Any ideas or suggestions
on how to minimize this from happening?

Can someone explain what happened?  Is this a common thing?  Is there a
potential for permanent hearing damage?

Thanks for any assistance.