What Causes Diarrhea And Vomiting In The Middle Of The Night?

My 20 year old daughter has been waking up in the middle of the night vomiting - sometimes accompanied by diahrrea. The symptoms are just like norovirus, but this happens nearly once a month. It has happened 6 times in the last 6 months. This lasts for 12 hours, and then subsides. Her stomach is so irritated that she dry heaves when nothing is left to vomit. Poor thing is just doubled over. This is also sometimes accompanied by stomach cramps. I assume a gastrointestinal problem because I have UC, but have never, never vomited because of it. Any help is very appreciated