There is generally a predictable pattern to flu recovery. There are, however, different ways in which the flu affects different people. Infections of the nose, throat, and lungs are caused by influenza (the flu). Flu symptoms vary from person to person. People feel sick for different lengths of time, and how sick they feel varies from person to person. There is generally a day-by-day progression of flu stages. When you know how the flu progresses, you can determine if you are contagious. It will also help you prepare to treat flu symptoms that haven't appeared yet by understanding the stages of the illness as it progresses. It is possible to wake up feeling fine on day 1, but you will experience the full effects of the flu by the end of the day. It is likely that these symptoms will arrive suddenly and without much warning. Keep hydrated at this stage with soups and water. You will feel the worst around day 2 or 3, but once you reach day 3, the worst is over. Your immune system is working hard to contain the infection during this stage, so you are less contagious since you are still in the contagious phase of the flu.