You know, he's always seemed kinda 'laid-back' compared to my previous B-boy, but he was 5 when I got him. I just thought, knowing a bit of his background (he was previously in a home with a special needs child), that he was just that way. Maybe he has had this thyroid issue for a longer time than it took to manifest itself, physically.
BTW, the backstory I heard for him involved a neighbor teen that was, supposedly, tortuous to the dog, ultimately leading to a bite. The dog and special needs child were best of friends. all of this could be 'horse hockey'….but even the vet has said he has a great personality.