Drooling dog on high alert

My 14-year-old female dog is acting very strangely. She is permanently alert, frightened, shaking and drooling, except when she is in her safe haven cage. Any advice would be helpful.

- DR DAVID GRANT

These signs are common in older dogs. The initial question is whether the problem has a medical basis or if it is behavioural. These signs suggest a possible psychological upset.