Along the lines of sinus pressure, CNS fluid stagnation in the skull may also cause migraine sufferers problems - need to see a good chiropractor to fix that, usually caused by C1 and/or C2 being displaced, happens to me frequently. Luckily it only causes visual migraines for me - have only had a disabling migraine once in my life when I was 18 at the TN World's Fair - some plant at our campsite caused a massive hay fever reaction - don't get headaches at all nowadays, only got them in my younger years from partying too much.