Unfortunately dogs are very prone to many of the same health issues we are and stress plays a very important role in this. My divorce years ago was very stressful and my dog suddenly started having seizures. The vet said that the stress caused epilepsy and he had to take anti-seizure medication for the rest of his life.
So unfortunately things like this can happen and they just snap. I'm sure it was a very difficult decision but probably for the best.
I feel your loss. I too recently had to put down a Jack Russell Terrier that was an extremely affectionate little doll. Except she started having violent episodes that made her dangerous. So I know that dogs can have mental issues. Making the decision to put her down was heartbreaking but necessary. Take comfort from the knowledge that you did the right thing and don't let the opinions of others cause you a moment of regret. You took the only responsible option available. God bless
Some years ago I had a cat have that happen. The vet said he was having small brain bleeds, he began to hallucinate and attack things that weren't there. What looked funny at first became dangerous as he forgot who we were....
I had this happen, also, to a golden retriever. She was getting steadily worse with her nervousness - she would chew the pads off her feet it got so bad.
We had to put her down when she became violent, too. She was the sweetest dog before that, too - best behaved dog I ever had. The vet was at a loss as to what to do with her - he said he'd never seen a dog chew their own feet pads off before.
I am so sorry you had to do that I know how heartbreaking that can be, I have 2 dogs I know in the future will have to be put down also. One with hip problems(a mastiff) and with mental issues as well. In her previous post she said the dog could harm someone so I would assume that is why her family came to that decision.