Recently I got a very ugly sinus infection - bad enough so that I've lost some significant ability to breathe through my nose. I can still breathe somewhat during spars, but if I have to use a mouthpiece for the hardcore stuff, whenever I bite for impact the ability to breath is gone and its hard to recover even from short bursts of not bringing air into my lungs. Seriously killing my MA since I cant really spar, just bag work.
If nothing else though, it sure teaches you how to avoid jaw shots. Do enjoy breathing AND not having my jaw broke in tandem.
- Op. Skinny Ninja