My two cats, one 19 and 11 months, died at home on the day we were due to visit the vet, and his brother, just 20 (same litter) was put to sleep yesterday when the vet discovered he had a tumour in his stomach.
Like your dog PinkCosmos he was sleeping most of the time but eating nothing and didn't seem to be in pain. It was a shock but we followed the vet's advice and had him put to sleep immediately, because he wouldn't recover; he was there with a vet he trusted, not having to make another journey in the dreaded cat basket, and died very peacefully.
Great sympathy for you, it is a horrible decision to make.