sounds like textbook hormonal imbalance and/or too many chemicals being released to your heart (acetylcholine, adrenaline, etc). You should get a followup because you don't want your heart to enlarge over the next 20 years or so by working so hard but unless there are other symptoms like irregular beats or passing out, your symptoms don't point toward anything troubling.
You condition sounds too complicated for me to directly relate, but I can say Metoprolol has been in use for a long time by many people, it is safe. I do not mean from that it is "good" for your body in any sense other than reducing you heart symptoms...if it does that.
I take high dose Metoprolol (200 mg) a day, and it does have some side effects, especially in high dose...you didn't say way dose you are taking. One of the side effects that can occure is dizziness, but I read you had that before starting Metoprolol, but it is my guess this medication can add to that problem, depending to some degree on what your blood pressure is. Metoprolol has two main effects: lower heart rate and lower blood pressure.