I went to stay with my sister for Thanksgiving. We both felt fine thursday, friday we took the kids to the zoo, there were 4 other adults with us. That night everything was great...about noon the next day my sister and I both are violently ill. Both of us vomited all day sat. into sat. night and felt so sick all day sunday not having the energy to move. Sunday night I could eat and get down fluids, monday the same, however monday brought on a pounding headache throughout the front and back of my head and nausea and fatigue...this has continued through today and I will be going to bed again tonight sick at 8:00 if I can make it that long. Neither one of us are pregnant, we ate the same things as everyone else, we are healthy 31year old women (twins). What could it be? There is no sore throat, no cold symptoms...