I will agree with the others. I saw shaking an panting in one of my dogs when she was very sick. Given the age, things can happen quickly. A geriatric blood panel and physical exam would be a good idea given these symptoms.
Older dogs can also get something called Canine Cognitive Dysfunction, something much like Alzheimer's disease in humans. My 14-year-old dog showed some minor signs of this in his last year or so. He would wander into a corner and seem "lost" and would cry. He also would wander and be more active at night. My dog was also deaf, so that could be part of it as well. I found this link helpful in explaining canine cognitive dysfunction, but you would also want to discuss the symptoms when you see the vet:
When my dog started doing the shaking and panting, I rushed her to the vet. She had several other significant health problems, but the cause of this was a severe, asymptomatic urinary tract infection. I know every trip to the vet at this age is scary, but you will need to get her checked. Good luck.