I would take this as a good sign that you are getting the yuckies out! Even if you were breathing freely before doesn't mean that you upper sinuses were good. The nasal drip was a sign that something was wrong.
I would liken it in a way to a detox reaction, but not quite. You are getting back into the infection and drawing it out. I don't see this as a bad thing. It means that what you are doing is working.