Why did my dog die?

My 15 month old lab started vomiting early one morning at first her dinner from the night before , after that just bile. she couldn't keep down water. she slept off and on and then seemed to be in a deep sleep. around noon without waking up she had a siezure. her eyes were open but she was completely limp. I rushed her to the vet . she had another seizure there then died. the vet siad she was very dehydrated and had very high blood pressure.she was fine the day before, eating, drinking, and playing.we did not have an autopsy done. what happened to my dog?