MUMBAI, 17 JUNE, 2021 (GPN): The biggest reason for post covid return is secondary infection or sepsis in lung, pnemonia with breathing difficulty with low oxygen saturation and clotting issues in the lung also known as pulmonary thromboembolism. Typicallly they come around 7 to 1t days post discharge complaining of fever and breathlessness with decrease oxygen. Mostly seen In  moderate to severe cases where prolonged hospitalizations makes them prone to secondary infection and underlying lung pneumonia and fibrosis makes it worse which compels them to seek medical care and hospitalization says, Dr Suleman Ladhani, Chest Physician, Wockhardt Hospital, Mumbai Central.