Hi Ghostie,
Not suffered from it myself but know a FO who has and says it can be very uncomfortable.
All i know is that there are two main categories:-
Acute (Short Lived) - A Cold or Flu
Chronic (more Prolonged) - Medical advice may be taken.
Here is a useful link from BUPA on the problem.
http://hcd2.bupa.co.uk/fact_sheets/html/Sinusitis.html
Here is a brief blurb on Sinusitis. "Sinusitis is inflammation of the linings of the sinuses (the bone cavities of the face) that surround the nose. Common symptoms include a headache and a swollen tender face." (BUPA Website)
Hope this helps. Good luck with it anyway.
Paul