- You can quote me
I can almost guarantee you it is nothing you did. I'll lay odds he had an undiagnosed and asymptomatic heart condition. Taking an unusually long time to come out of sedation, and then going into respiratory distress, is just too big of a sign. Dental problems are also often present.
But that doesn't really matter, does it? He's gone and it hurts, for you and for Jeeves.
Know that he will know he is loved always and never forgotten.