Your head is throbbing. Your throat is burning. You're coughing nonstop, and your whole body aches. This is no run-of-the-mill cold. You may have the flu. Let's talk about influenza, also known as the flu.

Winter is a time for sledding, snowball fights, and flu. Every winter, millions of Americans come down with this respiratory ailment and feel absolutely miserable.

Like the common cold, the flu is caused by a virus. But with the flu, it's the influenza virus that makes people so sick. The flu virus comes in a few different forms. Influenza A is most common between early winter and spring. You can catch influenza B year-round. Swine flu, or H1N1, is a specific type of influenza A.

You catch the flu from someone who has it. When people with the flu sneeze or cough, they send a spray of droplets filled with the flu virus into the air. If you're unlucky enough to be nearby, you could breathe in those droplets. Or, you might touch a surface that the droplets have fallen on and then touch your nose or mouth.

Two to three days later, the first flu symptoms will appear. Usually you'll start running a fever. Then you'll feel achy and tired. You may have the chills and feel sick to your stomach. After a couple of days, the sore throat and cough will set in.

So, how do doctors treat the flu?

Because a virus causes the flu, antibiotics won't treat it, they only kill bacteria. There are antiviral medicines, but you need to start taking them within the first 2 days after your symptoms appear.

Until the illness runs its course, help yourself feel better by getting a lot of rest and drinking extra fluids. You can take an over-the-counter cold medicine to relieve your congestion and cough. Tylenol, Advil, or Motrin can bring down your fever and take some of the pain out of your sore throat. Aspirin isn't recommended during the flu, especially under age 18, because it could increase the risk for a rare, but serious, condition called Reye syndrome.

By itself, the flu usually isn't harmful. But it can make existing conditions like asthma and breathing problems worse. In older people or those with a weakened immune system, the flu can turn into pneumonia, bronchitis, and other more serious diseases.

For most healthy people, the flu is a short-term annoyance. They're stuck in bed for a week or two, and then their symptoms go away and they're back up and around. But thousands of people each year get very sick from the flu, especially the elderly, young children, and pregnant women. Many are hospitalized, and about 36,000 people die from flu complications.

To avoid getting the flu, eat well, get plenty of exercise and sleep, and practice good hygiene. Wash your hands often with warm water and soap or use an alcohol-based hand sanitizer. Don't share cups, plates, or utensils, especially during flu season. And most effective, get your flu shot every fall to protect you through the whole flu season.