Influenza or "the flu" is a common viral infection of the respiratory tract. People spread the influenza virus easily.

Symptoms usually show from one to three days after exposure. Fever, chills, fatigue, runny nose, headache and muscle pain are the classic symptoms of flu, caused as the body fights the infection.

Influenza vaccine is helpful, but each vaccination only protects against a few strains of the changeable influenza virus. Severe strains are known to exist - a pandemic in 1918 killed millions of people.

Bottom line for deep sea sailors: Crawl into bed and ride it out. It's rarely serious, but expect to be debilitated for many days. And get your flu shot every year.