I can tell you for a certainty, my entire life has been plagued by flu symptoms.
When I was a kid, I remember that my mother had many flu symptoms which prevented us from enjoying a lot of outdoor activities. She couldn’t stand pollen and other outdoor allergens, so us kids spent a lot of time indoors. Ironically, about ten years later, I developed a terrible set of indoor flu symptoms, so I can barely stand my own house. As it happens, I am allergic to mold, mildew, dander, and dust. However, I did not at first realize that all of the indoor air contaminants were irritating my respiratory tract. For quite some time, I was coughing, sneezing, and blowing my nose all day long. Despite my attempts to mitigate them, no flu symptom medications or doctor appointments were fixing the flu symptoms that I was enduring. Eventually, I stopped trying to get answers from the medical community and turned to the HVAC business. I contacted the nearest air quality control specialist and he suggested an immediate emergency appointment for my entire HVAC system. When the technician got to my house, she immediately suggested that I try HEPA air filters and an advanced air purification device that would work in tandem with my installed cooling system and forced air gas furnace. By the time my heating and cooling addons were complete, I could breathe so much better. I came to find out what allergen had been irritating me the whole time. thanks to the heating, cooling, and air quality control specialist, not the expensive doctors I tried to get help from.