I'd be worried too if I were you. Sounds to me like he told you not to dive b/c of having to valsalva (or yawn, whatever you do to equalize pressure in your sinuses). Guess what, you'll be doing the exact same equalizing in the chamber, while flying, etc. But on the same page, it's not like you can go through life never equalizing your sinuses. This is definitely serious enough that you need to get checked out by a flight doc. If you can't chamber, you can't fly...sorry. But, it'd be better to find out now then to find out 4 days into UPT. Good luck, and if you want any hope of still being able to fly, stop boxing. Getting knocked unconscious is a 99% DQ (and don't say it'll never happen, b/c there's ALWAYS a high enough chance in boxing that it's not worth the risk).