My mate's Yorkie had a womb infection and was spayed by PDSA at about 11, she then developed cataracts and went a bit senile about that time. She lived till she was twelve, but was ex-Battersey and lived with an old woman who also went senile and my mate took her on when the old girl died. She had been mistreated in earlier years and only had one eye which kept getting infected, no teeth and a crooked front leg after being trod on by earlier owner and didn't receive any medical attention. She was very tiny and finally died of a heart attack. As her temperament has changed lately, perhaps it is senility or pain. I'd take her to your Vet get his opinion. Older dogs do tend to sleep a lot, but if she is interested in food, that's a good sign. Also she may have arthiritis, seeing as she doesn't like walks. Dogs are extremely good at hiding any pain (the survival instinct against predators) so I reckon a visit to your Vet might give you some insight. If you do, I hope it turns out OK.