Pomtzu- Do you think maybe if there were other dogs where you were that you brought back the scent on some of your clothes and it made Sparky anxious about another dog replacing him . Sounds weird that he would act like this after you've been back home for so long now, especially since he was at home with the rest of the family as you say. Maybe they get a bit more anxious as they age and it takes them longer to get over it. Hope he isn't coming down with something. Maybe try giving him extra attention for a few days to see what he does...poor thing, hope he gets back to normal soon.