I am sorry it took so long for you to get a reply.
How is your dog now? I know this was a week ago or more. Ears back and tail tucked usually mean either they have been scared by something or are not feeling so good. That is -if that behaviour happened suddenly, and isn't a normal habit.
If you can't figure out what might have scared him, then the other option is he is not feeling well, and a vet visit is the best plan.