If you're puking and have diarrhea, what you have is usually called 'stomach flu' which really isn't Influenza at all, but rather a condition more properly called viral gastroenteritis, which is caused by Norovirus and other bugs. --This is not to say when your immune system is compromised by gastroenteritis, you may be more susceptible to coming down with a case of influenza, as this has happened to me a few times before.
Influenza proper starts off resembling a common cold but with higher fever, muscle aches, or stiff/sore muscles and weakness, coughing and a runny nose. If you have severe influenza, after it clears up, you may wind up coming down with a secondary sinus infection that may or may not be viral induced, and could also wind up getting pneumonia as well, which is usually what kills you when you get the flu.
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