Losing pets is hard. "Restlessness and spinning in circles" sounds to me like possible symptoms of a stroke. Pets usually don't tell us what kind of discomfort they're feeling, so we have to make these kinds of decisions on their behalf. Our vet office has thanked me for not waiting on this kind of decision too long.
This is your call to make, and as long as you're making it with the best interest of your pet in mind, you will make the right decision.