Wow Warbird great to read your story...as it closely resembles mine...was in peak condition in my mid 50's in 2014 and started noticing slight decline in performance...and also when I am honest with myself the first signs of HR/arrythmias which I kind of ignored as I never was out of breath or dizzy...just HR spikes..and at times my heartbeat feeling disorganized while recovering on the sofa after a long ride/run....this continued on and off so much so that I moved away from Ironman level training after disapponting Lake Placid in 2017...continued uninspired "training" with only minimal HR disruption or at least that impacted me daily...until November of last year..when I went into Afib, Aflutters off & on continuously for a week ...kept me up at night,,,felt panicky during the day...I was supposed go on a business trip and my wife made me see the doctor before going...EKG picked up irregularity..put me into the hospital...Stress Test (with Dye infusion to rule out blockages)...and the Afib/Flutter was revealed....(thankfully no artery issues)....I also followed that up with heartmonitor for 30 days which showed I was in Afib for more often than I realized....lastly a sleep study to rule out any apnea as a trigger (negative)...and I chose right away for an Ablation...I didn't want rate control meds for life....I had the ablation on Wednesday this week...and recovering at home...tired, a little sore...but I love the sound of my heart in normal sinus rythm...I'm hoping for the same return to fitness you experienced...fingers crossed.