Signs and symptoms of dumping syndrome generally occur within minutes after eating, especially after a meal rich in table sugar (sucrose) or fruit sugar (fructose). They include: 
Feeling bloated or too full after eating
Nausea
Vomiting
Abdominal cramps
Diarrhea
Flushing
Dizziness, lightheadedness
Rapid heart rate
 Late dumping syndrome starts 1 to 3 hours after you eat a high-sugar meal. It takes time for signs and symptoms to develop because after you eat your body releases large amounts of insulin to absorb the sugars entering your small intestine. The result is low blood sugar. Signs and symptoms of late dumping syndrome can include: 
Sweating
Flushing
Dizziness, lightheadedness
Weakness
Rapid heart rate
 Some people have both early and late signs and symptoms. And dumping syndrome can develop years after surgery.