Did you check his glucose?
Could it have been a furball?
You can examine him for signs of infection, respiratory issues, malodorous breath ... anything you can check. Is he meat-loafing? Is he eating, drinking, eliminating, otherwise behaving normally?
Also, check the cans of food for the batch codes on them. In the fall, there can be significant changes in batches due to increased slaughter. These can be fast enough to cause GI upsets.