Emphysema is "a type of chronic obstructive pulmonary disease (COPD) involving damage to the air sacs (alveoli) in the lungs. As a result, the [body] does not get the oxygen it needs. Emphysema makes it hard for [the victim] to catch [their] breath. [They] may also have a chronic cough and have trouble breathing during exercise."
If untreated, emphysema sufferers often have so much trouble breathing that they must be put on a ventilator. The disease is often fatal, but the death is very slow and painful.