Final answer:
Paroxysmal nocturnal dyspnea is defined as acute shortness of breath that suddenly awakens a person from sleep. It is associated with congestive heart failure and can be relieved by sitting upright.
Step-by-step explanation:
Paroxysmal nocturnal dyspnea is defined as acute shortness of breath that suddenly awakens a person from sleep. It is a symptom often associated with congestive heart failure and is characterized by difficulty breathing, coughing, and wheezing upon waking from sleep. This condition can be caused by fluid accumulation in the lungs due to reduced cardiac function and is typically relieved by sitting upright in a chair to facilitate effective breathing.