I'm also allergic to corn (amongst other things). Like a previous poster, I'm not severely allergic, but my body definitely rejects it and I'm miserable until it's gone from my system.
Although life is harder now (I found out about the allergy about 2 1/2 years ago), I'm kind of grateful for it. I'm certainly healthier.
It's thought that people with allergies become allergic to the things that they are exposed to the most. If that's the case, I'm sure foods loaded with corn syrup are to blame for my allergies.
In addition to HFCS and corn syrup, other common ingredients I avoid are: dextrose, glucose, food starch, vegetable oil, and xanthan gum.