My dog has his tail under him, his hind paw in the air, not walking at all. When I went to touch his front paw, he went for me and wouldn't let go. He is a 3 year old, Full Male, chihuahua cross jack russel, all his puppy vaccines and 2 year vaccinations, weighs 7.1kg. What is thus, it only happened today, when he couldn't jump on the sofa, and now he can't move alot.