A fever can be the first sign that your body is fighting an infection. The body's regular temperature is 98.6 F (37 C). If your temperature is 100.4 F or higher on the thermometer, and you also experience difficulty breathing, chest pain, confusion, a bad headache, vomiting, abdominal pain, or signs of dehydration, you should seek medical care. In children, look out for the same symptoms, or for no change in temperature after medication and fluids have been given. Fussiness accompanying the fever, cold, clammy skin, and a very low temperature are additional signs you should get your child to a doctor.

Any form of chest pain, along with other flu symptoms, is a red flag. While it could be nothing, it may also be a sign of pneumonia, bronchitis, or even a heart attack. This isn't something to let slip, as the consequences can be as severe as death. If you experience chest pain, go to your doctor — or the ER — immediately.

A fever can spawn chills and "the sweats," but the key is how long you have them. If you've treated the fever and tried to let it run its course (as the sole purpose of your body's raising your core temperature is to fight off the infection) but you're still breaking out in cold sweats, the CDC recommends getting checked to rule out complications that stem from the flu itself (such as life-threatening sepsis, a blood infection that is particularly dangerous for young children).

Difficulty breathing is always a red flag — especially if you already have a respiratory infection or are asthmatic, as respiratory viruses can be the cause of severe asthma attacks. Asthma.net says if you have asthma, or a respiratory virus, you should have a plan of attack to help you breathe easier, even if it doesn't shorten the duration of the flu. Whether you have a pre-existing condition or not, sudden wheezing or difficulty breathing can be a major red flag that something's not right.

Chest pain with the flu can be a side effect of an infection or pneumonia or again, a heart attack (specifically in women, who may not have the typical signs you'd expect with a heart attack). When you're already dealing with the flu, don't dismiss chest pain as heartburn or something less significant.

Blurred vision, or loss of vision, is a serious condition that can stem from a host of things, such as glaucoma or stroke. Coupled with flu symptoms, it can be serious.

Conjunctivitis is common with colds and flu but, if left untreated or severe enough, can cause permanent damage.

A flu shot (for ear, nose and throat) doesn't help in the prevention of the stomach flu, norovirus. Health.com says that if you're having digestive issues like vomiting, nausea, or diarrhea, and the upset doesn't subside on its own, as it generally does, it is time to see a doctor. If you notice blood being regurgitated or expelled in stool, or experience lethargy or a fever of 101.5 F or higher, the need for medical attention is more acute.

In the event you have ear or jaw pain with the flu, you should seek treatment to be sure it's not an ear infection, strep, or tonsillitis (which have similar symptoms).

Neck pain in children can be a symptom of sepsis, and should be examined by a doctor, according to Made For Mums.

First, make sure you're not dehydrated, and ensure you are drinking plenty of fluids to aid in recovery. The flu takes a lot out of a person, causing you to feel more run down than usual, and not all symptoms are serious. However, you shouldn't ignore dizziness if it's accompanied by light-headedness, or any of the previously mentioned symptoms, such as fever or chest pain.

A refusal to take the bottle or breast in infants can lead to dehydration; no wet diapers for hours at a time and tear-less eyes are red flags that demand medical attention, per Dr. Sears.

If over-the-counter remedies aren't alleviating a headache, it may be time to have a visit with your doctor. Meningitis presents much like the flu, as the Daily Mail warns. Dr. Paul A. Offit, chief of the division of infectious diseases at the Children’s Hospital in Philadelphia tells the the New York Times that if your headache comes with a stiff neck, fever, or intolerance to light and nausea, you should seek medical advice to rule something more serious out.

For generally healthy people, the flu will come and go within around five to seven days, but could last up to two weeks. If you've had the flu shot, the duration may be shorter and symptoms less severe, according to Harvard Health. If you're still feeling the effects of the flu beyond the two-week mark, or if you have the extremes of any symptoms mentioned, go to the doctor.

Being trained to keep watch for red flags is helpful in pushing hesitant parents toward seeking a doctor's opinion. But the same virus may not present the same way in different people who are affected. As ABC puts it, "people often present 'atypically,' meaning that the symptoms they experience may be different than the textbook example." That means that you should be prepared to seek help even if you or your child don't show the "classic" red flags.

In itself, a "change in behavior," which might mean a disinterest in playing or general listlessness, is a red flag in a child. Floppiness or weakness is a definite red flag, as Made for Mums reports.

You are the parent: trust your instincts when you suspect something is wrong and seek medical advice.

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