Karlin wrote 'Be sure your vet is aware of some of the breed health issues such as episodic falling, epilepsy and syringomyelia.' You could add myoclonus to this list, which is becoming more common in Cavaliers and causes the body to twitch and jerk, which could be the 'shivering' you are seeing. It isn't painful, though my 6-year-old with it does sometimes look distressed.

Kate, Oliver and Aled (the one with myoclonus)