I am glad you went to the ER. I agree you were definitely overdoing it, but that is nice that you felt so good you thought you could! That also is good that they plan only to have you on the Amiodarone for no more than 3 months; that is what they told me too.
I hope this is not TMI - too much information, and am not a doctor of course, but just in case this is useful though, here is my story. I has been discharged after surgery with Amiodarone and Metoprolol, (and the anti-coag of course) and after a couple of weeks, I became so freaked out about the possible side effects I went off of the Amiodarone, prematurely. I then had A-Fib, had to go back to hospital first week of Feb for cardioversion, and went back on the Amiodarone. The good part is, this time both the surgeon and the cardiologist explained to me that the process of surgery itself causes some communication problems within the heart's own pacing system and that it usually gets sorted out within a few months. They reassured me that the really bad side effects become a concern if the patient takes the Amio for an extended period of time. They did check my liver and thyroid blood values in mid March. (Unfortunately, the thyroid issues can occur even with short term use, so make sure Docs are checking your thyroid status regularly.) I was told that the Amiodarone was for prevention of further arrythmias and that the Metoprolol was to keep heart rate from being too fast.
They had said they'd get me off the Amio ASAP and they did. My surgery was Jan 14. I was told it was OK to stop the Amiodarone at end of March (I had had an echo March 16). I had been concerned over really low BPs during the cardiac rehab exercise process, discussed that with the cardiologist via her nurse, and got the OK to taper off of Metroprolol second week of May. You've probably already Googled Metoprolol and found that you must not stop it abruptly?
My BPs have remained in normal range since getting off both drugs, but my heart rate is a tad fast on any exertion (resting is OK 66 - 78) but any exertion puts it into 84 - 90 zone. I hope that will improve, and if I recall correctly, that is probably due to my having left ventricle enlargement. I had found out through my research on Metoprolol side effects that it is known to disrupt sleep patterns, and inhibit the body's production of melatonin. I am thrilled to be off of the Metoprolol though, because I am sleeping better.
The main danger of too much of the beta blocker is 'bradycardia' or unusually slow heartbeat. So, if you continue to notice slower heart rate than ideal, that would be something to discuss with your Doctor.
Edited to add, electrolytes being out of optimal range can trigger arrythmias too, so if you recently (as I imagine you did) got CBC, electrolytes done, get a copy of that report, and ask Doctor when they are going to check those again. They may already know, from having monitored you while you were in for the surgery and now for the Afib, whether you have any trends out of range. For example, if your potassium gets too low that can be an arrythmia trigger, same with magnesium. Too much potassium is a bad thing too, so might be a good idea to have Docs tell you how many milligrams of potassium you should be consuming per day.
