Dumping syndrome is a pain in the stomach, where you feel bloated, maybe you vomit, maybe you have nausea, maybe you will experience having a cold sweat, maybe you have palpitation, you feel the need of lying down and maybe you get diarrhoea.
If you have some of the symptoms above you should be careful with foods and drinks/liquids containing large amounts of sugar, lactose (sugar from milk) and fruit sugars (fructose).