The achiness and fever also signal that you need to start drinking a lot of fluids. The battle royal being waged inside you will dehydrate you more than you think. You may notice that your urine will get darker and you’ll have to go less often. Experts say to make sure you drink a cup or so of water or other liquid every hour, avoiding alcoholic and caffeinated beverages.

Drinking fluids will diminish your headache and also bolster your immune response because your protein soldiers are conveyed via bodily fluids. Dehydration hampers their movement. It’s one reason people tend to want soup when they’re sick and may crave watery fruits like citrus and melon.

While you may feel rotten all over, the real battle is going on in your respiratory tract where the virus is localized. When the war is winding down, you stop feeling achy and feverish but you have residual inflammation in your throat, sinuses and bronchial tubes. All those cells lining your mucous membranes have been damaged and are like weeping sores, Dr. Schaffner said. That’s why your nose is runny and you start to sneeze and cough to clear out the detritus.

Given this, over-the-counter medications that suppress your cough and dry your sinuses may not be the best idea.

“Certainly there is the thought that you don’t want to suppress a cough too much or dry out your nasal passages because you want to get rid of the infection,” said Dr. Tara Vijayan, an assistant clinical professor in the division of infectious diseases at the University of California, Los Angeles, David Geffen School of Medicine. “There’s a balance for sure. I don’t think you should suffer unnecessarily, but you need to weigh the true benefit.”

Although you want to rest, lying flat all the time can be problematic because it collapses your lungs so you can’t cough as efficiently, trapping bacteria in your respiratory tract. If the virus destroys enough cells in your bronchial tubes it creates openings for bacteria to get into your lungs, which can lead to pneumonia, a potentially life-threatening complication of the flu.

When your lungs are vertical rather than horizontal, “you’re able to breathe deeply and freely and you’re able to cough out any inadvertent material, even microscopic bacteria, that get down into bronchial tubes,” Dr. Schaffner said.