It's possible that you have what is known as Mitral Valve Prolapse Dysautonomia (may also be called Mitral Valve Prolapse Syndrome, Orthostatic Intolerance Associated with Mitral Valve Prolapse, or POTS/Postural Orthostatic Tachycardia Syndrome Associated with Mitral Valve Prolapse).
To be evaluated for this, you likely need to see a specialist at a major teaching hospital, usually a cardiologist (especially an electrophysiologist-cardiologist) or a neurologist with knowledge/experience in autonomic disorders and orthostatic intolerance syndromes. Your doctor may be able to give you referral.
A tilt table test and possibly Holter monitoring may be useful in helping to make this diagnosis, along with some targeted blood labs and urinalysis (things that would not have been done as part of a normal CBC panel).
You will need to talk with your doctor about what symptoms should warrant a trip to an ER; this varies depending on the patient.
Here is more information on getting a diagnosis and our further reading section which has articles on various types of autonomic dysfunction:
http://www.medhelp.org/health_pages/Neurological-Disorders/Diagnosing-Dysautonomia/show/827?cid=196
http://www.medhelp.org/health_pages/Neurological-Disorders/Autonomic-Dysfunction-FAQ/show/181?cid=196
http://www.medhelp.org/health_pages/Neurological-Disorders/Dysautonomia-Specialists/show/717?cid=196
http://www.medhelp.org/health_pages/Neurological-Disorders/Dysautonomia---Links/show/744?cid=196
http://www.medhelp.org/health_pages/Neurological-Disorders/Further-Reading-on-Dysautonomia/show/696?cid=196