Out of the blue, Jas just started shivering and tucking his tail between his legs. DS was stroking him at the time, but not in a scary way (he's 12). Obviously, DS stopped and called me. The dog got up on the sofa next to me, burrowed under my arm and shook like a leaf for 20 minutes. I have no idea why. He has now taken himself off to hide under the dining table. No obvious illness, gums a good colour, no vomiting or diarrhea...Any ideas? 