There are many reasons why a dog might experience vomiting or diarrhea. Vomiting and diarrhea could be secondary to something as simple a dietary indiscretion but could be symptoms associated with a more serious medical condition such as a toxin ingestion, inflammation of the pancreas (pancreatitis), an intestinal blockage, or parvovirus. These medical conditions can result in fatality if left untreated. If your pet is experiencing severe vomiting or diarrhea, seek veterinary care immediately.