Last avmed training I did, they said it is a normal response to an abnormal situation.
Apparently eating poisons will upset your vestibular system first (think head spins when drunk & laying down), so we have evolved to vomit in response to crazy vestibular vibes (correct, I *don't* know medical lingo).
Anyway the good news is that anybody can be trained to learn the experience. Just don't be physically sick as your body will (incorrectly) learn that is the best way of dealing with it.
The best thing ($$ dependent) is to knock off the flight if you are physically sick as you won't be learning anything & probably causing you to think it's a terrible job, where as in fact if you give it A few flights you'll love it!