LOL, they can be scary.
Before I retired I had multiple episodes of arrhythmia that caused rapid heartbeats (170+bpm), tunnel vision and the occasional blackouts. After multiple heart tests involving EKG's, Echo-cardiograms, ultrasounds, etc., the cardiologist said it was a common afib type problem that is often caused by stress and anxiety. It is not normally life threatening in a healthy person with no blockages, etc. He put me on medication to control my heart rate along with Wellbutrin for anxiety and stress.
Well, I decided working in a high paying stressful job until I was 62 was not that important. I retired at 58, have lost 30 pounds so far since I'm not working up to 80 hours a week, and have NO more arrhythmia's. I'm off of all of the medications. Stress can cause these issues but if Fuddy was in otherwise good health, it's very doubtful that she would have died from the irregular heartbeat. The times that it is fatal are caused by blood clots that cause a stroke and that would have shown up in the autopsy. I do take an aspirin a day to eliminate that possibility in the case of an arrhythmia. Irregular heartbeat is not normally life threatening, according to my cardiologist, if it occurs in the upper part of the heart as it is if it's in the lower part. Afib is the most common and least deadly, according to him.
The big problem with a-fib is the probability of a blood clot formimg. You normally go on a blood thinner.