Oh, man, how scary for you, Bastien!
Just a thought--we've had similar reactions here to mushrooms. Not all of them that spring up in the yard are 'bad', but our Ridge always manages to find the funky ones.
The only treatment is supportive IV-fluids to flush the kidneys. And, of course, she always manages to find them at night or on holidays so it involves an emergency trip to the vet afterhours... *sigh*
Any chance Bully could have found a bad mushroom? I know they're popping up all over our yard now after our wet week. We're sorta crossing our fingers and sweating it out till things dry out...