
It could easily be just the association between the fireworks and darkness. My dobe boy is the same - not as bad, but once the fireworks start he'll only go out after dark to pee, does it as quick as he can and is usually difficult to persuade to do it. He's not afraid of the dark much indoors, but when I go to bed he'll lie there alert, looking at the window, worrying about noises that may or may not be happening. He won't do that if the light's on, at least not usually.
After tonight he'll be even worse - some blummin moron (and that is in no way close to the words that are in my head, or came out of my mouth - loudly - in the garden earlier) let off a huge firework just after dark earlier, when he was outside. And he was so much better than last year so far. Ar$eholes.