Diarrhea is a very unspecific sign and it may be related to several diseases.
Acute diarrhea is usually caused by infectious agents (bacteria, viruses), abrupt dietary changed or inappropriate food. Infectious causes of diarrhea requires antibiotics while feeding-related diarrhea requires only correcting of feeding errors. Emergency treatment and supportive therapy may be required in most severe cases.
Chronic diarrhea (lasting more than 3-4 weeks) can be caused by several factors like parasites, food allergy, problems with food absorption from intestines, pancreatic diseases, liver problems, tumours in the gastro-intestinal tract. Chronic diarrhea can be more difficult to treat and often requires additional tests and investigation.
It is not an emergency condition but it may be a sign of a serious disease.