What Does Severe Fatigue And Shortness Of Breath Indicate?

My husband has been in excellent health, but in the last couple months has developed extreme fatigue and shortness of breath. He went and got oneof those heart screenings where they do a bunch of test for $150, at a location, be use we were Otha worried about it. They called him 3 days later and said he was in constant aFib. Pulse 120-130. So he went to our MD and he ran a battery of tests also, ekg, chest eras, echocardiogram, and blood tests. They saw fluid on/in his lungs, and verified that what the heart screening said was correct. Dr put him on aspirin, lasik, and potassium. We saw a heart specialist 4 days later. My husband was still in aFib, owever the heart dr said other than that, he was healthy according to his echo and blood tests. My husband was put on Elequis and sotolal. They then set him up to get an ekg, swallow a camera to see inside the heart and then shock the heart (if still in aFib) 2 weeks later. Well this is all to happen on this coming Tues Sep 5th. (Sorry so long) but here is my question. My husband feels even worse on the medicine(Elequis & sotolal). He s been on it 10 days. He can hardly catch a breath, has trouble climbing the stairs. He can tell he s still in aFib, but his BP and pulse are good. The fatigue is awful. Also, he is coughing up mucus that looks like brownish or blood tinged. We did call heart dr last week to ask about how lousy he felt and was told that is normal side effect of medicine until you get used to it. He didn t mention the mucus to the dr because this is a newer development over last couple of days. Could there possibly be something else going on with him, like cancer or something and that is causing the aFib? He was going to wait until Tues at his appt. to speak w the heart Dr about that. What is your thought? (Husband is 6 2 , 235 lbs, never smoked, drinks occasionally- semi retired). Thank you, TML