What are the main causes of shortness of breath? 1. anxiety. anxiety is one of the main causes of shortness of breath in people who don’t have any other health problems. when faced with an anxiety attack, a panic attack, or highly stressful situations, the sufferer may feel short of breath or feel like they are suffocating. hold your breath, the total air in the lungs does gradually decrease, so you become slightly less buoyant near the end of a breath-hold but for most people, the only way to really sink is to exhale a bit to get to negative buoyancy being extremely lean can make the body sufficiently dense that a person is negatively buoyant, even when holding a full breath being lean also helps you to stay under water longer because, if your lung volume remains constant, decreasing your overall weight means More healthy lungs but short of breath images. Causes of sudden shortness of breath. sudden and unexpected breathlessness is most likely to be caused by one of the following he...