What condition is characterized by shortness of breath when lying down?

The condition characterized by shortness of breath when lying down is orthopnea. This specific type of dyspnea occurs when a person is in a supine position and often improves when they sit or stand. Patients with orthopnea may require pillows to prop themselves up while sleeping to relieve their symptoms. This condition is commonly associated with heart failure, where increased venous return from the lower extremities when lying down can lead to pulmonary congestion, exacerbating shortness of breath.

While dyspnea is a general term for difficulties in breathing, it does not specify the positional nature of the symptom. Apnea refers to a temporary cessation of breathing, which is not related to shortness of breath in a lying position. Tachypnea indicates rapid breathing but does not specify the conditions under which it occurs, such as lying down. Thus, the focus on the positional aspect of shortness of breath in orthopnea makes it the most accurate answer.