I had sinus surgery in 1985. Had polyps and constant sinus infections, and my septum was deviated. I had "windows" but in to let my sinus drain properly. (I now have two more holes in my head than most people. Explains a lot, don't it?) I remember I healed VERY fast, but much of that was my Dr's technique - as I recall, she'd come up with a little plastic thingie sewn through my septum to splint it. Sounds painful, but it wasn't. The worst part was when she removed the rubber drain tubes that were protruding attractively from each nostril. I say "removed" but the process involved her putting one hand on my face and yanking with the other. For about 2 tenths of a second, it felt like she was pulling an anvil from the back of my head using barbed wire. Then, all better.

She also told me not to sneeze. Like I had a choice.

I wasn't singing at the time, but if it happened now, I KNOW I would have felt the difference. Your sinuses are part of the sound system, and when it's right, you can actually feel the vibrations in them. More air, less obstruction, is good.

Did you have tubes down your throat during the surgery? Those are likely to temporarily affect the voice