My mom's event was caused by a rare, underdiagnosed syndrome called Brugada syndrome. In addition, she was on Flecainide for her afib which can bring on dangerous arythmias in people with Brugada. Of course, the doctors didn't know at the time they prescribed Flecainide that she had Brugada. She most likely never would have had an event if she wasn't on the drug.
Anyway, her anxiety was a result of her cardiac arrest, not the cause.
I don't know the answer to your question about what the 8 fast beats mean. But if the doctor was worried about it, they probably would have had you in for an EP study or at least followed up. I know it's easier said than done, but try not to worry too much about IF and WHEN something will happen to you. It takes a lot of enjoyment out of life and at 17, you're most likely safe and should be having fun! Sometimes I wish I was 17 again.