I had post nasal drip long before Lyme.
Ironically, I didn't realize it had improved until after I lowered the dose of NAC I'd been taking as part of Buhner's protocols. Needless to say, I'm back to the higher dose :)
The stuff thins mucus:
www.livestrong.com/article/492669-n-acetyl-cysteine-for-mucus-in-the-body/among many other benefits:
www.lifeextension.com/magazine/2010/5/n-acetyl-cysteine/page-01