I was diagnosed with atrial fibrillation several years ago. It is not a disease; you don't catch it from other people, like flu. It is, therefore, a condition. 'Critical illness'? I don't know about that. If I hadn't been diagnosed (by a ECG machine) I wouldn't have known that I had it, and I doubt that I have it now. Yes, I have been told that it can lead to the problems that you describe. I was offered medication, at the time, but I declined them all. If I still have atrial fibrillation, I don't know it, so I don't do anything about it.