The odds are that the upper part of your cage might be a tad warm for your chameleon. Just double check the temps! Also listen closely to the breathing. If you hear extra clicking or wheezing sounds it may be a upper respiratory infection!
Like @Matt Vanilla Gorilla said listen for the sounds but just FYI Veilds will open their mouths during basking. Make sure you have plenty of options for it to be closer or further from the lamp so they can choose the temp. My veiled will always go for the one that's the highest and sit there with his mouth open. I have seen several other people on here say the same thing when it comes to veiled but not many with panthers.