What does it mean when i feel really ill after eating icecream or sweets?

its weird i cant be a diabetic because i eat potatoes and pasta just fine and the have sugar in them and i have sweetener in my tea ect, but sometimes i would eat some sweets and after feel really ill dizzy sick and hot iv felt like it before when iv read for a long time in a car its horrible and takes over an hour to ease, earlier i ate some ice cream a fair bit lol and straight after that horrible feeling came over :( is it simply a sugar overload?