There are many ways one can fake an illness, with some methods more effective than others. The most common and popular trick is one we’ve all heard of — simply holding up a thermometer to a lightbulb in order to fake the impression of having a fever. The potential downfall of this method though, is that these days many thermometers are checking temperature through the ear as opposed to the mouth and can be completed in a matter of seconds. This method was much more effective back in the day when thermometers took much longer and there was more time to accomplish the task at hand.
The good news is that there are many other avenues one can use that don’t involve thermometer props. Decent acting talent and a dedication to the role are all you really need. If you have the time to plan it out, start mentioning the day before your illness is supposed to take effect and mention how “tired” or “sluggish” you’re feeling. Many illness take some time before coming on full force, so mentioning that you’re not feeling well the day beforehand sounds much more feasible than a sudden onset of flu-like symptoms.
Some other ways to play up your illness is to give the illusion of cold and clammy skin. This can easily be done by merely splashing some cold water on your face, making sure to get the front of your hairline as well. After this you can walk around (slowly, of course) talking about how warm you feel. This will give the impression that you are experiencing cold sweats, a telltale sign of an illness. You can also reverse this trick and use warm water on your face giving a flushed appearance while complaining about how cold you are.
While attempting to fake a stomach illness of some sort, it is always wise to spend a lot of time in the bathroom. If you are in there for an extended period of time, most people will not question what it is you are doing in there because they really do not want to know.
The most important thing to take away from all of these tips is that the less you play it up, the more believable it is going to appear. Making a huge scene out of anything is going to make you look much more suspicious. It does not need to be a huge production and always remember that less is more.