Gastroenteritis is a medical condition in which GI tract is infected by the bacteria or virus. It is also known as stomach bug or stomach flu.
Symptoms typically include both diarrhea and vomiting, with or without abdominal pain or cramping. There may be low grad fever. The diarrhea can be watery usually without blood. The bloody diarrhea (dark red or black colored) indicates the severe infection or the complications of other infection.
It can heal itself in most cases in a week. If it lasts more than a week, or you have vomiting for a day without food/liquid intake, please go to see your doctor. See you doctor right way if you are vomiting blood or having bloody diarrhea.