My first dog, Sheba, had spent some time on her own as a stray, and even had puppies then, best as the vet could figure. She was a brave, brilliant dog - who was absolutely terrified of thunderstorms. She HAD to climb up into my parents' bed whenever we had them, which in the summer was quite often, poor thing. The vet always guessed she had been outside during a bad one when she was a stray, so we just cuddled her and let her know it was okay.