A collapsed lung, or pneumothorax, happens when air gets into the space between the lung and the chest wall, which makes the lung partially or fully collapse and can make breathing difficult. It can be serious, especially if the collapse is large or symptoms come on suddenly.

What you may feel

Common symptoms include sharp chest or shoulder pain, shortness of breath, chest tightness, and sometimes a rapid heartbeat or lightheadedness. A larger collapse can cause bluish skin, near-fainting, shock, or severe breathing trouble.

What happens in the body

The air trapped outside the lung creates pressure that prevents the lung from expanding normally, so oxygen exchange drops. In some cases, the lung may collapse again later, and serious complications can include infection, respiratory failure, or heart failure.

How it’s treated

Treatment depends on the size and cause of the collapse: a small one may just be watched, while a larger one may need a needle or chest tube to remove the extra air. Many people recover well with treatment, though doctors may monitor you in the hospital.

When to get urgent help

If someone has sudden chest pain, trouble breathing, blue lips or skin, fainting, or worsening symptoms, it should be treated as an emergency.

If you want, I can also explain why it happens , how doctors diagnose it , or what recovery looks like.