Last night while eating (I emphasize that because with this particular dog, that's an important part of why what follows is so W.E.I.R.D.)...
... Max abruptly ran away at full speed barking his fool head off and trailing a slew of crap behind him.
He ran from one end of the house to the other, crapping and barking the whole way. He appeared to be completely oblivious to the presence of anyone.
We let him outside immediately where he zipped around the backyard, still barking but not crapping, still oblivious to the presence of anyone. We could not catch him. Unfortunately he found a spot to escape and ran off to the front yard. Fortunately he seemed to want to run a perimeter so he came back around the backyard gate that I had opened to get out so I could meet up with him in the front yard. Mind you, at this point, I am not completely oblivious to the fact that I am barefoot and in PJs.
Max ran through the gate still barking like a madman and uncatchable. He ran around the yard and came back to the gate area, where between our gate and the neighbors house there is a space of about a foot where we installed chicken wire to seal up the yard. He didn't see the barrier. He threw himself into it at full speed and literally bounced off of it, leaving behind an impressive dent. He did this at least four times.
Finally he calmed down.
What set it all off is still a mystery.
He looked seriously deranged through it all. And even in the end, his mane was so full of burrs that he was the perfect canine image of the madman with messed up hair. Both ears were firmly attached to his neck. We still haven't successfully removed all of the burrs. They cover his head, ears, neck, feet, belly.... Mr. Field Notes succeeded in detaching his ears from his body.
An obvious trigger for the sudden freak-out would have been Katy making a move for his food. He's very possessive of his food and even if Katy had made a move, which in itself would be surprising, his response would have been to attack her, not tuck tail and run off so scared that he trailed poo. Even so, Katy was not the trigger - she was calmly eating her food when it happened. It was as if a monster so grand and horrifying the likes of which no one has ever seen suddenly appeared out of nowhere to frighten the living daylights out of Max and only Max.
Our vet had no idea about what could be the problem but he suggested we take Max off the Rimadyl he started last week for his arthritis. I don't have any good guesses about what the problem was. He does have a history of subcutaneous cysts, tumor like lumps that are harmless, but now I'm wondering if he has a tumor on or near his amygdala. That would go a long way to explaining his increasingly aggressive behavior.