What condition is characterized by shortness of breath while lying down flat?

The condition characterized by shortness of breath while lying down flat is orthopnea. This phenomenon occurs when a person experiences difficulty breathing in a supine position, leading them to seek relief by sitting or standing. It is often associated with heart failure, as fluid may accumulate in the lungs when the individual lies down, increasing pulmonary congestion.

The other terms related to breathing difficulties are distinct from orthopnea. Dyspnea refers more broadly to the sensation of difficult or labored breathing, which can occur in various positions and is not limited to lying flat. Apnea describes a temporary cessation of breathing, and hypopnea indicates a reduction in breathing depth or rate, neither of which specifically pertains to the positional aspect of shortness of breath in the way orthopnea does.