I think there's a chance that it could be the food - I'm allergic to coke, but not diet coke or pepsi. We've even tested it because a friend thought it didn't make sense. Over a period of a few days he would put JD in with various black coloured soft drinks from diferent makers - I couldn't tell which drink was which, but sure enough, an hour or so after drinking the JD and coke I was vomitting.
Or it could, as you say, be that flying and eating don't mix for some people.