Hi,
There can be many reasons directly involving lungs and/or heart, or indirectly those organs through allergic reactions, side effects of medicines etc. You can get more details from the following link :
http://www.hopkinsmedicine.org/heart_vascular_institute/conditions_treatments/conditions/shortness_breath.html
Solace
Hi,
You should urgently see a doctor for appropriate diagnosis and treatment, as it is a serious issue.
Solace