Does my dog know that he is dying?

I have a chihuahua papillion mix. He's an older dog. The vet told me that he's dying. He's not suffering right now, I will have him put to sleep when the time comes.

But I've noticed that he has been extremely affectionate recently in ways he never was before. He sat on my lap in the computer chair which he's never done before. ~10 times a day he'll come in from another room and just walk up to lick my face. He lets me hold him without pushing up against me to get out of my arms. I can tell he's getting tired.

I've heard some animals understand the concept of death but I'm not positive on that. But this behavior change is making me wonder... does he know he's going soon? Is he being more affectionate to tell me he loves me one last time? Or is this just a coincidence?

Sorry for the sad topic.