You're really over-thinking this- please do hold off on vet appointments until you have a really good reason to need one -they're stressful for your snake, & obviously you too. Let your snake eat & digest a number of meals in peace- stress is bad for everybody's health- & please keep an open mind about the state of your snake's health. Plenty of snakes will lay around (not moving) for days at a time (especially when they're digesting, OR, in a shed cycle) and it doesn't mean there's ANY thing wrong. I've kept many (!) snakes for decades (not this species) & staying low-key & just "TLC" (good food & good environment) can do wonders for keeping snakes healthy- that's how their immune system functions best.
And by the way, as a life-long "dog companion", I feel your pain & I'm very sorry about your dog's diagnosis- especially for only being 6 years old- that seems so unfair. I'd be a mess too, about that.