Norovirus = sickest I've ever been in my life. Twice. Maybe psyop, but what I said stands. Comes on quick, like 10 - 12 hours and then the fun begins as you turn your insides out.
The diarrhea is so bad and prolonged if you don't rehydrate with electrolytes and get a dose of lomotil, you're at serious risk of death. Then there's the non-stop vomiting. Ice machines are frequent sources if not cleaned well.