My dog was panting earlier, went out for walk, did a couple of loops around the field and he was fine doing his normal sniffing and running after scent. Got home and a few hours later he was shivering. He sat by back door and went outside and lay down. he's moved off his bed onto the cold wooden floor, walked outside, done a long wee, moved across lawn and sat down. I'm going to take him to the vet first thing but has anyone got any ideas?