I'm so sorry for your loss, and now that you say the eyes sunk in suddenly, I believe that it was illness. Your husbandry looks good, so don't think that it was your fault, unfortunately, if you keep Reptiles in really good health, you will have to part with them eventually. If you get a chameleon in the future, I would change to a different calcium/multivitamin schedule as Reptivite has preformed Vitamin A, which can be overdosed. Again, I am really sorry for your loss, hope the little guy rests in peace.