Few sensations are as frightening as not being able to get enough air. Shortness of breath - known medically as dyspnea - is often described as an intense tightening in the chest, air hunger or a feeling of suffocation. Very strenuous exercise, extreme temperatures, massive obesity and high altitude all can cause shortness of breath in a healthy person. Outside of these examples, shortness of breath is likely a sign of a medical problem. If you have unexplained shortness of breath, especially if it comes on suddenly and is severe, see your doctor as soon as possible.

Causes
Most cases of shortness of breath are due to heart or lung conditions. Your heart and lungs are involved in transporting oxygen to your tissues and removing carbon dioxide, and problems with either of these processes affect your breathing. Shortness of breath that comes on suddenly (called acute) has a limited number of causes, including:
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Asthma 
Carbon monoxide poisoning
Cardiac tamponade 
Heart attack
Heart failure
Low blood pressure
Pulmonary embolism
Pneumothorax 
Pneumonia 

Self-care
-- Stop smoking. Once you're tobacco-free, your risks of heart and lung disease and cancer begin to drop - even if you've been smoking for years.
-- Avoid exposure to pollutants. As much as possible, avoid breathing allergens and environmental toxins.
-- Lose weight if you are overweight.
-- Take care of yourself. If you have an underlying medical condition, take care of it.
-- Have an action plan. Discuss with your doctor what to do if your symptoms become worse.
-- Keep elevation in mind. Avoid exertion at elevations higher than 5,000 feet (1,524 meters).
-- Regularly check your equipment. If you rely on supplemental oxygen, be sure your supply is adequate and the equipment works properly.