Just to help in the future, because I personally cannot have artificial sweeteners, there is a difference between being allergic to something and having a reaction to something. I get a reaction which is severe muscle pain and headaches that last for days, but fortunately it's not life-threatening.
A true food allergy affects the immune system. Even small amounts of the offending food can trigger a range of symptoms, which can be severe or life-threatening. In contrast, a food intolerance often affects only the digestive system and causes less serious symptoms.
It's important that they know what is life threatening to you. Some lines will actually let you choose your menu the night prior so that they can prepare your food based on your needs. I hope you are able to work everything out.