While there is no one reason for the two symptoms to strike, we do know that novel coronavirus can launch a multi-pronged attack on the respiratory system (chest, lungs) as well as render the immune system deficient. COVID attack can also ruin the healthy cells along with the lung linings, making you prone to infections, breathing issues and in some cases, can even cause scarring. Researchers have also now found that the virus could impact the respiratory system in a big way, and cause problems like lung fibrosis, in the long term, even in the healthiest of patients. Infections, such as pneumonia can also cause these symptoms in the long run.
Symptoms of lung fibrosis, at the earliest level, could also impose problems in regular breathing and impact the blood oxygen levels in the body. Hence, some patients are asked to continue using oxygen support machines (oxygen cylinders, concentrators) for a while post recovery to regain regular strength.