Think my dog is showing signs of cognitive decline - how will I know when it's time to make the call?

[MagliaRosa]

He's a 13 year old (very big) lab, he's had arthritis in his hips and spine for years, recently he's had real trouble getting up and in the last few weeks I've had to actually lift him most of the time.
Along with this he's also started whining/crying at night, gone off his food a bit (unheard of for him!), messed in the house, keeps getting himself stuck awkwardly against furniture or in corners.
I'm taking him to the vet soon but reading up it does seems it's probably dog dementia.
I was wondering how long we may reasonably have left with him now - do they decline quickly with this or could he stay the same for months? That's probably a bit of a how long is a piece of string question!
It's so upsetting to think about having him PTS but I know I'm going to have to make that decision at some point. I don't know how I'm going to do it though, he's my baby.
I guess I'm just asking for stories from others who've been through this so I can prepare myself better.

There is medication for dog dementia, one of our dogs had it and he was much better for a short while with the medication. We had our most recent dog PTS earlier this week, he was also very arthritic and couldn't get up without help. Despite Tramadol and metacam he seemed to be in pain and he had a sunken head on one side and bleeding from his right nostril, which is not good. I couldn't decide what to do but was swayed by an article which suggested you should make a list of the 5 things the dog liked best and look at whether he could still do them. Our dog wasn't enjoying his food, had given up snoozing in the sun in the garden and couldn't manage a walk. He was also very distressed by his mobility problems. I might have chickened out and kept him a bit longer but DH talked sense to me and said it was cruel and for our own purposes only. WE did the right thing. Our vet was very good with explaining the options, but in the end there really weren't any.

Thank you, I think the list of five things sounds like a good way to think of it. Sorry to hear you lost your dog recently. I will see what the vet advises about if medication would help for a while but I've really got a feeling we've not got long left with him. He is getting a lot of cuddles at the moment.

I recently lost my 19 year old cat who was fine up until the day before he was pts . The intense heat in June killed him. I went to speak to the vets before we made the call and she said something to me which I've since repeated a few times and it was the perfect words ..she said '' it will never be too soon but it is often too late '' . It was exactly what I needed to hear because I did not want him to suffer . He went peacefully on my lap in my bedroom with a lovely vet and all his family around us . It was as lovely as it could be . I would always recommend you get the vets to come to the house and allow you to spend time with them when they have passed . Don't rush saying goodbye x

Sorry to hear about your cat imjessie. That does sound like another good piece of advice. Thanks.