Psychological

• Anxiety frequently leads to chronic and acute hyperventilation. Often associated with panic attacks, this state of rapid breathing increases carbon dioxide in the body and limits the flow of blood to the brain, which ultimately can result in a feeling of breathlessness.
  
  

Heart Disease

• Shortness of breath is one of the most common indicators of a heart condition. These disorders can include, but are not limited to, heart attack/failure, arrhythmia, congenital heart defect and diseases of the heart's valves.
  
  

Lung Disease

• There are numerous conditions that can reduce the lungs' capacity to transport oxygen and carbon dioxide to and from the body, and therefore trigger feelings of shortness of breath. The most common lung disorders include pneumonia, bronchitis, croup, pulmonary hypertension and various fungal infections.
  
  

Airway Obstruction

• Perhaps the most obvious obvious cause of shortness of breath, airway obstruction, can occur anywhere from the nose and mouth, to the trachea, to the bronchial tubes and tiny airways within the lungs. A blockage can occur by suddenly inhaling a solid object, food particles or liquid. It also can result from a swelling of the glottis caused by an allergic reaction.
  
  

Other Common Causes

• Obesity, high altitude, low-oxygen environments, allergies to pollen, dust, or mold, and hiatial hernia all can cause shortness of breath. Also, acidosis, such as the type that results from aspirin poisoning, can result in the feeling of not being able to breathe.