Depends on etiology
The two most notoriously missed conditions are<unk> pendicitis and small bowel obstruction.. When discharging patients with<unk> , clear instructions should be given for return if there are red flags.
Abdominal pain
Abdominal aortic aneurysm
Nausea and vomiting 
Aortocaval fistula
Nausea and vomiting
Acute gastroenteritis
Diffuse abdominal pain
Aortoenteric fisulta