Hello ! Lung collapse can be caused due to many reasons ranging from a mere mucus getting plugged in your airways to a foreign body getting lodged in your airways n blocking them to a growth encircling or growing within the airways to fluid or air getting accumulated around in the lungs (in the pleural space ) passively collapsing your lungs. Hence kindly review with your physician and get to know what had caused your lung to collapse and whether the collapsed lung had now expanded back to it's normal form . Not all shadow on a x ray indicate something ominous. So don't jump into any conclusions. Rather discuss with your physician and if needed you can get CT chest done for further evaluation.