Ate a lot of pecans on an empty stomach and have been nauseous for two hours. Why?

I ate a bagful of candied pecans and I had felt perfectly fine throughout the rest of the day, not tired or nauseous or turned off to food. I was pretty hungry, and I ate the entire bag without a second thought. Then about five minutes afterward I became extremely nauseous, as though I was severely carsick. The feeling has lasted almost three hours without going away very much. Why is this happening?