My almost 8 year old female Berner, Bonney, seems to sleep an awful lot. I would say that on average, she sleeps 20 hours a day. We take her for a walk every morning and in the car with us whenever we are going anywhere or running errands. We are home with her so there is always activity around her. She just doesn't seem to want to play or do much. Is this normal for a Berner her age. She eats well, goes to the bathroom fine...has a slight tear in her CCL but we are monitoring that. She is on medication for the knee injury but this amount of sleeping started before she went on the meds. Thoughts?