Does this sound like Anxiety? There is a strong association between stress and cardiovascular disease. They can also be a outward exhibition of post traumatic stress disorder. I can smoke and then exercise and still have all my lung power.
Stress can cause just about every symptom you can imagine. Best also get a stress test to see if there might be other problems. Having a feeling of impending doom.
Anxiety can indeed cause the heart to beat irregularly. If you sweat a lot you best get your potassium level checked. Atrial flutter is an abnormal heart rhythm that occurs in the atria of the heart causing abnormalities and diseases of the heart. My suggestion is to see a psychiatrist and get treated for the hypochondriac disorder.
Many of the symptoms you describe could be related to anxiety. The symptoms can be very scary and can actually cause you to feel like you are going to die. Women who are enthusiastic to conceive are mostly scared with the term miscarriage. Most symptoms are present due to stress or some type of an event in your life. Maybe if you can get over that hurdle it will help.