My Boxer died in January. She was in pain and couldn't walk and we found out it was cancer in her anus which spread to her back bone and her lower back bone had disintergrated. She was panting for a whole day before she got really bad and couldn't walk and we thought she was possibly sick and as a result really hot. No vets were open (public holiday) so we gave her a bath, put her in air conditioning and in front of fans etc but she didn't stop panting. When we went to the vet, we found out that heavy panting of this nature means they are in a lot of pain. We had no idea. She was put to sleep the next day. Just thought I would warn and inform people just in case it ever happens to them.