<human>: Can you summarize the given text in a few sentences?

I have a yorky that's around 7 years old.
He likes my dad and hangs around him a lot cuz I'm not home due to college. But for the past 4 days he's been really tired and basically acts like a grandpa. He has no energy at all to do anything, he just lays on the bed with his eyes open. He has troubles walking straight and exercising which he usually never does anyways;;. He's kinda obese, but not like crazy obese. Nothing changed in the way he lives or how we treat him at all, so we have no idea why he's like this.

My wild guess is that his lungs are giving out.
He had troubles with his lungs ever since he was a puppy,
the vet told us he had very small lungs and that he needed to be careful.

But my dad smokes a lot;; and he's been smoking in and out of the house ever since we got the yorky...could this be the issue?

Did the yorky get cancer or something? Like lung cancer?
or maybe he got diabetes cuz he's overweight (i don't think this one's that realistic cuz he's not that fat...he's just a little fat).

Or maybe he's just old?
But the weird thing is he has never been this tired looking, it just started recently.
<bot>: Dog acts like he's a zombie/dying. Doesn't move around a lot. I think he has lung cancer due to dad smoking way too much around the dog. Is this possible?