paroxysmal nocturnal dyspnea

Paroxysmal nocturnal dyspnea, often shortened to PND, is a sudden attack of breathlessness that jolts a sleeping person awake, typically one to three hours after going to bed. People describe waking gasping, fighting for air, sometimes coughing, and rushing to sit on the edge of the bed or open a window before the feeling slowly subsides over tens of minutes.

The mechanism resembles that of orthopnea but is slower and more dramatic. While the person sleeps flat, fluid gradually pools back into the circulation and the lung vessels, and the depressed nighttime breathing drive lets carbon dioxide and lung congestion build quietly. At a tipping point the congested lungs and the suddenly roused brain combine into an abrupt sense of suffocation. Unlike simple orthopnea, sitting up does not bring instant relief; it can take half an hour or more to settle.

PND is most strongly associated with left heart failure, where it is a worrying sign of worsening congestion. However, nocturnal asthma, COPD with overnight secretions, and obstructive sleep apnea can produce similar nighttime awakenings, so the description must be weighed alongside other findings rather than taken as proof of any single cause.