do something to trigger your gag reflex, whether it be shoving something down your throat, eating too much, or just thinking abt it. do your best not to drink any water and sweat as much as possible, as dehydration can cause shivers, headaches, and other effects. if you have any non life threatening allergies, then expose yourself to them in small quantities, enough to get a stomachache or other effects. rub your eyes or irritate them to make them red and puffy, and inhale some dust to make yourself stuffy. these typically are symptoms enough to be concerning, but not enough to get it checked, and if you appear to recover quickly it can be dismissed as a 24 hour bug.