7. You have no appetite.
Let’s be clear: just because you ate five slices of pizza last night and now you’re not all that hungry does not mean you are sick or you need to play hooky from work. But if you are unable to keep any food down then you run the risk of becoming dehydrated and malnourished. You will become weak and you won’t be able to fight off whatever illness is calling your body home. Best to stay home, rest up, hydrate, and save your energy.