Maybe the acid that comes up aggravates the mucus membranes???
I had post-nasal drip for a long time and I have some allergies and sinus problems that started about 15 years ago. I couldn't take it anymore, so I started nasal irrigation (Neti pot) because my yoga instructor had mentioned it once and thought it was worth a try. It has helped me a lot. I don't know if it would do anything for anyone else, but I haven't had to take sinus meds since December which is a miracle for me. I don't have the drip anymore either.