From watching animal planet so much, I think that it means that your dog's temperature is a little bit too low. But that channel also says that dog's temperatures range anywhere from 100 to 107.
My dogs temp is 99.0 but he is laying here out of it and his nose is really warm. Its like he is really tired and wont respond. It happens every now and then and I have taken him to the vet multiple times and they say there is nothing wrong with him he is a perfect healthy dog. It just really scares me and I don't know what to do anymore.