There are different types of fribilations. Some are considered worst than others. If they have you hooked up to the machine when it happens, they can an idea of exactly the type. I had the least worst type. I think it was ventricular fribilation? Anyway it would cause my heart to just race even thought I was just sitting or doing nothing strenuous. It would then subside. I had three in two years and would just lie down and hold my breath to get it to slow down. the third time cause it was at work they had to call the amb. where they injected with something to sedate and slow it back down. In some cases I heard the emergency crew will have to inject you with something to literally make your heart stop, not slow down but stop, then shock your back to life to reset it. For me it was a kind of short circuit as the doctor explained it to me. A signal would tell the heart to pump, when it shorts its like doubling or looping the signal and the heart pumps faster when it don't needs to. How bad it is depends what is pumping and opening and closing (valves) to fast or slow. the bad fribs, I guess can end up causing clots and eventually strokes or other.
I was given the choice of meds or a Catheter procedure where they snake the catheter up near the groin area to your heart to the area that is bad (with another set of catheter having a camera. they then use a kind of use a sound wave that is suppose to burn or open the short circuit that developed on your heart. I chose that as I don't want to end up taking so many meds when I get older cause you never know about side effects and how it mixes with other meds. It was funny was awake the whole time and was trying to see the lcd screen and see what i look on the inside, but didn't want to move and cause a screw up, haha-the lcd you cannot see when you are at an extreme angle.
Anyway, if you guys ever get where your heart races for no reason check it out, don't mess around, catch it early, as the more serious ones they can cause a clot and stroke.