Influenza is a viral respiratory infection characterized by fever, cough, headache, fatigue and inflammed respiratory membranes. Although nausea, vomiting, and diarrhea can sometimes accompany influenza infection, these are rarely the major symptoms.
Influenza is much more serious than the common cold.
Cold and flu symptoms resemble each other, but differ in intensity. A cold generally begins with some minor sniffling and sneezing and causes generalized discomfort. A cold rarely moves in to the lungs, whereas the flu can cause pneumonia. You may be able to drag yourself to class with a cold, but with the flu, you'll be too ill to leave your bed. The most telling symptoms are fatigue and muscle aches which are normally absent with a cold.