I saw this posted elsewhere on Facebook and have added it to the thread in the health library section on how to know when the time is right to let your beloved cavalier go. It's a helpful view from a vet:
http://www.naturalholistic.com/download/Dr_Bernstein_Holistic_Care_Saying_Goodbye.pdf
http://www.naturalholistic.com/download/Dr_Bernstein_Holistic_Care_Saying_Goodbye.pdf