Oh, Anglebrite, I am so terribly sorry to hear that.
I have no idea what it could be, but please, call your vet and talk to him (or her) and take your other dogs in to make sure they haven't gotten into whatever it was. Please, do this just as soon as possible. It really could make a difference between your other dogs surviving and not.
I can truly have sympathy for your feelings. We lost our Buffy when she was just two years old to someone who fed her meat laced with antifreeze. The grief is so awful, and then to have to worry about your other dogs and wonder if you will lose them too is just horrible. I worried for a long time that Bimmer might have taken some of the poisoned meat, but fortunately, he's always been good about not trusting anything that I don't give him or he doesn't hunt down and kill himself.
Do check with your vet. It might even be some type of snake bite, although I've always been told that snake bites don't affect dogs as virulently as they do humans.
I am so, so, so sorry that you are going through this terrible experience. No one should ever have to deal with losing a pet this way.
Renee