What do you think is wrong with my dad?

Hi, happy new year everybody. So last year my dad got a minor heart attack and is on medication. Hes been pretty good except for the past couple of months.. he's got the flu last month and was battling a lot symptoms feeling (runny nose, cant breathe, productive cough) he went to the doctor the first time and they gave him inhalers, nasay spray and codeine.. which he took for 2 days (the codiene) as he said the inhaler will give him more heart problems. His symptoms have cleared up but I find now he's cant sit still, says he has anxiety and feels like he cant breathe at times. He never tells me what the doctor says and I'm scared he has cancer or some lung disease :( I know you guys are not doctors but what would u think it is, what should he do? Have u guys ever had this happen.. hes really ignorant and doesnt wanna go to the doctor.

Update:

Just to add too he's 51 and smoked for atleast 40 years.. recently stopped last year following his heart attack

Update 2:

Another thing to add too is we recently got a gas stove... read online that can cause anxiety