Some dogs are good at hiding pain.
Simon was an indoor dog if you can believe that. Towards the end I had to actually carry him outside 3 times a day so he could do his business. He had "Degenerative myelopathy " which, ( at that time ), was almost unknown. It was/is common with big dogs. It is like hip dysplasia, only worse. Death is 100%, but they do not experience any pain. My son's German Shepherd had the identical condition. Luckily, he lived near Ames and they have a very good Veterinary College Program so he took her there 3 times a week. Swimming was something she liked to do there, even though she wasn't swimming. They place her in a pool with a special life vest on. She could do the dog paddle to help work her hips, it probably lengthed her time with my son by maybe 6 more months and it got to the point that she would look us in the face as if to say " I am ready ". Sad, but life is not always fair. Cherish the moments and take A LOT of pictures. You probably won't want to look at them for a while, but sooner or later you will and it will remind you of all the good times and make for great memories.
We did that too. I or my wife would carry him outside, he'd just sit there, take him in after about a half hour, and he'd go on the floor within seconds of being in. ANd the poor dog would bow his head and look down because he knew he was supposed to go outside. He would have good days where he'd get up and go to the door. But, within seconds would go right in front of the door.
on a side topic...One of the coolest things I've ever seen with animals. My wife has a cat. It would sleep right with the dog when he started getting sick. That cat would run to the dogs food bowl get one piece of food in it's mouth and run back to the dog and drop it by his head, over and over. I've never seen anything like it. The cat would groom him too. After the dog died that cat got real mean and is still mean today!!!
My wife and son are the only ones that can touch it. It will very rarely let me pet it. When our son was born he had a real rough start and had some medical issues. he was born 10 weeks early and luckily grew out of them for the most part. The same cat, even though she's old now, would lay under my sons bed And if he started making noise it would get nervous and start meowing at my wife.
Her cat even though I hate it because it's so mean to me

is an amazing creature.
Another thing about that cat that is amazing, most anyone that tries to pet it, it rips into you. I mean chomps down on your hand and shakes it's head with no warning, will claw the crap out of you. I tell everyone that walks up to it"don't touch that thing, it will rip you up!!!" And usually they don't believe me because it looks so nice and acts like it wants you to pet it, they get bit bad!! My son is 3 now, he has grabbed the cat by the tail pulling it across the carpet, he has tried to pick it up by it's head, sits on it, etc...The cat has never bit, scratched or even hissed at him! We try to keep him away from it just in case but it's nearly impossible and the cat doesn't seem bothered by him. Even now it sleeps within feet of him... I can't even pick the thing up without getting tore up, I have to get my wife to do it. Really strange how it took to our son. It also doesn't get along with any of the other cats in the house except one, and it's a special needs cat. It will groom him and protect it from the other cats.The Re tar ded one is mine!
Animals are amazing at times, My dog was like a part of me. He knew when you were sad. It really sucks when they get old. It's like a family member leaving too early.