What term describes difficulty breathing when lying down?

The term that describes difficulty breathing when lying down is orthopnea. This condition is often associated with heart failure and certain lung diseases, where the individual experiences increased difficulty in breathing when they are in a reclining position. In contrast, dyspnea refers to general difficulty in breathing, which can occur in various positions and is a broader term that does not specifically denote the posture-related aspect. Dysphagia pertains to difficulties in swallowing, while dystaxia refers to a lack of coordination in movement. Therefore, orthopnea accurately captures the specific challenge of breathing that occurs when lying down, making it the correct answer.