Now that you have lost him, and since you have another chameleon, you seriously need to review your husbandry. I would start by double checking temps, making sure there is nothing they can ingest, and be getting a fecal done on your panther. They could have contracted a parasite via feeders. Also make sure there are no unusual fumes (hairsprays, paints, insecticides, etc.) since this seemed to be a very sudden death.