I would suspect some type of bacterial infection.

I'm so very sorry to hear about the loss of your friend's dog. I hope they get the answers they are looking for.

I'm very sorry for your friend's loss. I know of a chocolate lab who had similar symptoms. Fortunately, it happened when he was at the vet for a heart clinic and they got him through it. His episode was blamed on apple seeds. He apparently ate a bunch of apples from a tree in his yard and had a severe reaction.