You feel like you have been hit by a tonne of bricks. You ache all over. You have a sore throat, a headache, fatigue. You alternate between feeling like your body is freezing and boiling. Perhaps you have a cough, a sore throat, and even a runny nose.

You have the flu. This year’s H3N2 or Australian influenza, is particularly nasty.

And then, just when you think you are getting better, your bout of the flu seems to return. In reality though, the second act is not usually the flu. As it departs, the influenza virus can leave people open to other infections.

“The flu is a changeling,” according to Sherilyn Sweeney, a professor in Kwantlen Polytechnic University’s nursing program. “It’s a repeat customer for many people.”

Influenza wallops the whole body, including the immune system. The virus can drop your defences, leaving you vulnerable to a second bug. The flu can cut the number of neutrophils in your body. They are an important kind of white cell.

“Neutrophils are our first line of defence,” says Sweeney.

This temporary dip in the immune system offers a window of opportunity to bacteria and even other viruses which can cause things like pneumonia or sinus infections in people who might have otherwise fought them off.

The influenza virus can also damage the microscopic hairs lining the airways.

“The cilia in our breathing tubes are like brooms in charge of sweeping everything out again, keeping our airways clean. When they can’t do their job, those viruses and bacteria can sneak around, heading down to our breathing sacs,” says Sweeney.

She says that once in there, deep in our lungs, it’s an ideal place for bugs to grow, making us sick, making us short of breath.

“We don’t exchange oxygen as well if (infections) settle down into our air sacs.”

So, how does one prevent these bacterial infections that can crop up just as the flu seems to be passing?

First off, Sweeney suggests, get your flu shot to prevent influenza in the first place. It’s the best of defence.

“Remember that it takes up to two weeks to work so there’s a bit of a lag time,” she says.

Since some of the symptoms of influenza are from your enraged immune system, you can feel a bit “off” after having the immunization because, even though it contains no live virus, the vaccination riles your immune system, teaching it to fight off the real thing.

Though the flu shot isn’t 100 per cent effective, it can mean you get less sick if you do catch influenza because it boosts your immune system to better fight off the virus.

Sweeny suggests additional preventative measures: “I think it comes down to taking care of yourself. Get the sleep you need. Eat good nutritious meals. Drink good fluids. Wash your hands regularly and, if possible, stay away from people who are actively sick.”

If you do get the flu, and you are otherwise healthy, Sweeney’s advice is adamant, “Stay home.”

She adds:“I don’t think we take time to be sick anymore. We don’t take time to take care of ourselves, to be gentle. We take medicine that just makes our bodies feel better instead of staying in bed, taking care of ourselves and allowing our immune system to do its job. We are often our own worst enemies.”

And has Sweeney had the flu?

“Yes, I have, last year. I felt like my chest was heavy, very hot and my eyes were burning.”

While most people, as Sweeney did, recover from the flu on their own, some people can have life-altering or life-threatening consequences from the virus itself or from the bacterial infections that may follow.

For that reason, Sweeney is clear, if the patient is elderly, very young, or someone with an underlying condition, be sure to have them seen by a doctor if they come down with what might be influenza.

There are prescription medicines that can cut the severity and duration of the viral infection but they need to be started right away.

If you are in a high risk group and come down with the flu, “Go see your doctor, just to get checked out,” Sweeney says.

How do you know if you might have a bacterial infection right after you have had the flu?

Sweeney says if you feel like you are getting better then things get worse, or just hang on, that means something else besides influenza might be coming on. She also says a high fever can be an indication of problems brewing so seek medical advice.

She counsels listening to your body. She says you have to know what’s normal for you so that when things are abnormal, you know to see your doctor.

Sweeney advises erring on the side of caution.

“Make sure you stay on top of it. Far better to go in and have the doctor say, ‘It’s just the flu hanging on,’ instead of saying, ‘We wish you ‘d come in earlier.’”

Some cases can require antibiotics to get rid of a bacterial infection.

While the flu’s damage to your defenses are usually temporary, in the frail, young, or already ill, the effects of these secondary bacterial infections can be life-long or worse, deadly.

The Public Health Agency of Canada says though the reported cases underestimate the true numbers, there were 11,277 laboratory-confirmed cases of flu across the country up to the end of December, with more than 1,000 influenza-related hospitalizations and 34 deaths. Those numbers are expected to rise as flu season peaks.

So, to give you the best chance of getting better and to protect others who may be hit even harder by the flu and all of its consequences, Sweeney’s advice is clear.

“If you’re sick, take care of yourself. Stay home.”