My old english sheepdog has dementia, he has bowel movements in his sleep or just walking through the house. He has muscle weakness now which according to the vet, is just like older people who lose muscle strength. (picture older humans using a walker).
I read an article in whole dog journal that says giving them Sam-E is supposed to help w/the dementia. I haven't tried it yet to give you advice but, may be worth to do a little more research and give it a try.
I haven't taken my old guy in to the vet either as I know what is coming down the road and no amount of pills will help right now. Been there done that with my last two. My hound made it to 17 and my female OES died within a month of a diagnosis at 10. I do have on hand some pain pills from the last two if he seems too uncomfortable.
Sometimes you are damned if you do and damned if you don't. Good luck!