Hello and thanks for writing. I can understand your concern and would try to help you in the best possible way. Your complaints suggest you have mitral valve disease and your cough is related to it. You are having symptomatic mitral valve disease like light-headedness, fatigue, cough and Atrial fibrillation (heart rate of 256). I suggest that you should not take these things lightly and consult a cardiologist who will help you with a long term management plan which may include lifestyle changes, management of comorbidities and certain medications. You need an evaluation of condition of your mitral valve by an echocardiography.