Rapid gastric emptying, or dumping syndrome, happens when the lower end of the small intestine (jejunum) fills too quickly with undigested food from the stomach. "Early" dumping begins during or right after a meal. Symptoms of early dumping include nausea, vomiting, bloating, cramping, diarrhea, dizziness, and fatigue. "Late" dumping happens 1 to 3 hours after eating. Symptoms of late dumping include hypoglycemia, weakness, sweating, and dizziness. Many people have both types.
Certain types of stomach surgery that allow the stomach to empty rapidly are the main cause of dumping syndrome. Patients with Zollinger-Ellison syndrome may also have dumping syndrome. (Zollinger-Ellison syndrome is a rare disorder involving extreme peptic ulcer disease and gastrin-secreting tumors in the pancreas.)
Doctors diagnose dumping syndrome primarily on the basis of symptoms in patients who have had gastric surgery that causes the syndrome. Tests may be needed to exclude other conditions that have similar symptoms.
Treatment includes changes in eating habits and medication. People who have dumping syndrome need to eat several small meals a day that are low in carbohydrates and should drink liquids between meals, not with them. People with severe cases take medicine to slow their digestion. Doctors may also recommend surgery.
source: http://digestive.niddk.nih.gov/ddiseases/pubs/rapidgastricemptying/index.htm