Final answer:
Paroxysmal nocturnal dyspnea is a type of breathing difficulty that occurs at night during sleep. It is associated with heart failure and fluid buildup in the lungs.
Step-by-step explanation:
Paroxysmal nocturnal dyspnea is a type of breathing difficulty. It is characterized by sudden episodes of severe shortness of breath that occur at night during sleep. This condition is often associated with heart failure and occurs when fluid builds up in the lungs.