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You should get medical help as soon possible. Do not hesitate to call the ER or call ambulance. This could be the manifestation of a cardiac failure. (among other possible causes ). As this is an emergency you should medical help as soon as possible.
Generally this could be due a Cardiac cause, Respiratory cause, or a Neuromuscular cause.
The symptoms that you have described of passing out on standing could be due to a drop in your blood pressure known as othostatic hypotension and it needs evaluation. To give you a more learned opinion I would like you to answer some questions. How would you describe the chest pain? was it sharp,squeezing or a heaviness? Have you been on any medications for hypertension diabetes, heart problems, or depression? Have you conducted any blood tests like fasting blood sugar, lipid profile recently and were they normal? Have you had any fever or cough with sputum?
2)Cardiac Biomarkers (must)
3)Brain Natriuretic peptide
4)Arterial and venous Blood Gas
5)Carbon Dioxide Monitoring -To see your ventilatory status.
6)Pulmonary Function Test -If all of the above come normal.
Kindly do not ignore your symptoms and do take help and get yourself evaluated immediately. Meanwhile lie down. You may also call your friends or family for help. I will keep this consult open indefinitely. So you please get in touch with the ER. Once the acute event is stabilised you can get back to me for followup.