A collapsed lung happens when air enters the pleural space, the area between the lung and the chest wall. If it is a total collapse, it is called pneumothorax. If only part of the lung is affected, it is called atelectasis.
Causes of a collapsed lung include
If only a small area of the lung is affected, you may not have symptoms. If a large area is affected, you may feel short of breath and have a rapid heart rate.
A chest x-ray can tell if you have it. Treatment depends on the underlying cause.
NIH: National Heart, Lung, and Blood Institute