My buddy may be dying

I'll do everything in my power and spare no expense to save him, i just wonder if he's given up, saving his strength, recuperating, or what he's thinking. He wags his big old tail up and down when i go in to see him. I had to cup water in my hand and hold it under his mouth for him to lap, he was pretty thirsty, won't eat yet.
Wagging tale is good.
Maybe Zeus is suffering from what all creatures go through when they get their butt whooped.
Either way I'd get him to the vet for a checkup.