I had that happen to me, the day before I was coming home for Xmas when at University. Best mate, Spike the cairn terrier, after 14yrs of chasing rabbits and eating everything he could lay his paws on finally passed away. He barked at the postman one last time and fell asleep next to the radiator.
It really broke my heart but at least he was always healthy & had a good innings. Think of the good times you had together, and think of it in a place where it's always walk-time, endless rabbits to chase and as much chocolate as it can eat.
Really feel for you chap......