Originally Posted by Velo Dog

Scary as that is, it's probably not that big a deal. I went into fib 15 years ago, at age 44. At the time I was running 40-60 miles a week, and my times increased literally overnight from 6:30-7 minute miles to 8:30-9. I went through all the tests, tried electrical cardioversion, but wound up solidly in fib, where I've been ever since.