I have 4 grand-dogs, I can call on their owners for advice.
Ruby started shivering about an hour after her walk, despite having a coat on after being towelled down. She kept running from room to room, kicking out one back leg as soon as she settled down. After conversing with DS, several times, he concluded it was either cramp or muscle spasm. An hour later, she is asleep, almost shiver free and seems better, phew!