We have some friends looking after our house and our pets while we are away. They brought their dog, who did not get on with ours. The two dogs did fight, and in the fight one of our friends got bitten. Then out of the blue one day when he went to pat her on the head, our dog snapped and then attacked him. He said he fought her off and hit her to get her off, she collapsed and died very suddenly. He said he did not hit her hard, just to get her off. Our dog can be a bit snappy when food is around or if her bad leg is touched, but she has never attacked someone, our little girl loves her and is always cuddling her. I think she was very stressed that we had left and new people with a new dog had moved in. Any idea what would have caused her to act like this and attack, and then died so suddenly?