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Winter's arrival and the drop in temperatures that come with it means it's a good time to take stock of what to do – and what not to do – when you're feeling sick.

Colds, influenza and other respiratory illnesses tend to be more common during colder months, when viruses spread more easily because people are indoors more and in closer proximity to others. So far, doctor's offices and hospitals across the U.S. have been busy, said Dr. Trish Perl, a professor of internal medicine at UT Southwestern Medical Center. Physicians at the Dallas hospital have been "quite active," she said, and not just with cases of respiratory syncytial virus, or RSV.

"There's an increasing amount of influenza going around," she said. "Even in the past week we have seen the numbers increase, although it is unclear the trajectory, and it's notoriously unpredictable when it emerges."

The coronavirus that causes COVID-19 also tends to spread more during colder months.

for the flu, RSV and have been elevated or increasing in recent weeks, according to the Centers for Disease Control and Prevention.

If you come down with a respiratory virus, here's some advice from medical experts that can help you feel better and protect others.

DO: Stay hydrated.

Blood is comprised of 55% plasma and 45% cells. Blood plasma is made up of over 90% water, and a healthy blood pressure is important to deliver oxygen and nutrients throughout the body.

Drinking water helps your immune system by circulating blood volume, said Dr. Pei-Ni Jone, a pediatric cardiologist at the Ann & Robert H. Lurie Children's Hospital of Chicago and a professor of pediatrics at Northwestern University's Feinberg School of Medicine. Noncaffeinated drinks and hot soup work, too.

Staying hydrated is based on individual needs and varying conditions, but in general, men should consume 13 8-ounce glasses of water per day, nine for women, according to the . Keep in mind hydration can also come from water-rich foods, especially fruits and vegetables.

DON'T: Eat salty foods or consume alcohol or drink caffeinated beverages like coffee and soda. They can lead to dehydration.

Jone said staying hydrated while fighting a virus is "critically important" because the fluids help blood circulation, which can "help carry the immune cells throughout the body."

DO: Stay warm. Sounds logical when you're sick, and there's a good reason behind this tip.

Viruses like influenza, the coronavirus and RSV can cause a fever, Jone said. "Fever is a sign that the body is fighting these viruses, and patients will have chills related to the fever. Staying warm will reduce the discomfort of the chills and help circulate blood to carry the immune cells to their destination."

Jone said it is OK to take fever-reducing medication to make you feel better.

DO: Speaking of sleep, it's important to get plenty of rest.

Sleep gives your body a chance to heal and let your immune system work. Seven to nine hours of sleep a night is ideal for adults. "Sleep is actually quite important when you're ill because the more you sleep, the better you recover," Jone said.

DO: Wash your hands with soap and water and practice good hygiene, especially if you live with family or friends. If you must leave the house while you're sick, also wear a mask.

If soap and water aren't available, a hand sanitizer that contains at least 60% alcohol also works.

"Hand hygiene decreases transmission to other people," Perl said. "And don't forget to wipe your counters and other hard surfaces that viruses can survive on."

If you have symptoms before heading to your workplace, consider colleagues who might be immunocompromised. Work from home, if possible, Perl said.

DO: See your doctor if symptoms persist or get worse.

There is no good rule of thumb in terms of how many days to wait before seeing a health care professional because the course of an illness may vary for each person, Perl said. Sometimes, someone might develop a high fever right away, and in those cases, you should generally seek medical care. Most secondary infections following viral infections occur five to 10 days after one first contracts the illness, she said. The flu can make someone feel sick for up to a week.

"You want to use your best judgment" when determining when to see the doctor, Perl said.