The flu (influenza) is a viral respiratory illness that causes fever, chills, runny nose, body aches, and cough. It spreads easily from person to person. The flu can cause moderate to severe symptoms.| medlineplus.gov
Weakness is reduced strength in one or more muscles.| medlineplus.gov
Pain is a feeling triggered in the nervous system. You may feel it as a prick, tingle, sting, burn, or ache. Read about the causes and what can help.| medlineplus.gov