Recognize the Symptoms: Symptoms of influenza include cough, sore throat, runny or congested nose, body aches, headaches, fatigue, and sometimes fever and vomiting. While flu symptoms are often similar to cold symptoms, a key difference is the sudden onset experienced with the flu. If you suddenly experience some or all of these symptoms, you may be contagious. Stay home and rest, so you can heal and avoid spreading the flu. If you suspect that one of your friends has the flu, encourage him/her to limit contact with people, as well.