I have to agree with Jerry_NJ. You need to make an appointment with a doctor to see exactly what is going on.
It sounds like you need a check-up with a doctor, at least a primary care that does electrocardiograms...my GP gives me an EKG when I get my annual physical. I also have a cardiologist, but then I have diagnosed heart problems. ..some fixed, some I just live with.
Some things you can do to get an idea is to check your pulse rate (over 50 bpm at rest best) and blood pressure. If you HR is very low, like below 40 or your BP is low, that could be the condition that is causing your symptoms. How to fix it is another matter, and best if a doctor makes a recommendation.