5. Flu
When we think of the flu, we tend to think of symptoms such as running noses, coughing, sore throat, and more affecting the sinuses. In fact, though, flu can affect the entire body as it is a simple infection.
The symptoms that you experience are actually caused not by the infection itself but rather by your body: this is your body trying to drive out the foreign invader. As a result, it raises its temperature to make your body less habitable and it can also cause symptoms of nausea and sickness to try and encourage you to vacate your stomach and bowels to remove any offending critters.
This is why the flu can actually make you feel sick to your stomach as well. To solve this issue, try switching your diet to dry and salty foods. Drink plenty of water, get lots of rest, and listen to the advice of your doctor to help drive out the illness.