Thank you both @Jyoti and @Pistolfor your warm welcome and support!
Since I have been competing in swimming for the past ten years, it has been a work in progress to figure out what my body needs and how it responds to different work loads. Just when I thought I had it nailed, these past several months have told me otherwise.
I haven't yet received a specific diagnosis other than "autonomic disorder," so I'm sure that is what Dr. Snapper will figure out. Exercise intolerance doesn't seem to be an issue, though, as long as I keep my heart rate below 80% of max-- something I have recently figured out. I've been able to make that connection after monitoring it frequently throughout my workouts. Where I run into trouble is if I DON'T exercise at all or overdo it with too much speed. My swim training for each day is dictated by how I feel during warm-up and how my heart rate responds at warm-up speed. Today, my heart rate was up 18 bpm swimming at the same speed as on Saturday-- unusual, since I take Sundays off from the pool. As a result, I backed way off and just swam drills. On other days, I can crank up the speed with a lower heart rate, and those are the days I feel great. I backed down my weekly swimming yardage (and intensity) to swimming six days per week maxing out at 2,500 yards per session, and that has helped. Some days, when I don't feel right, I call it quits at far less yardage.
Over the past couple of months, I have come to realize that I will need to swim my races within my heart rate tolerance (and how I feel) rather than "racing" my races. I'm signed up for two meets next month, and I am mentally prepared to do just that. I don't want to miss out, because the meets are so much fun and not about winning. Most of us compete against the clock rather than each other, but I am prepared to let go of my time goals and just have fun in the pool. I recently competed in the Georgia Games Open Water Meet and swam three races (2k, 1k, and .5k), just cruising at a comfortable speed, and I recovered beautifully! (I also ended up with 2 golds and 1 silver medal as a nice bonus!). That might not be the case at future meets, though, so I am prepared to bail out of races if I don't feel right.
For me, it seems like how my body feels is tied in with my heart rate. When I don't feel right, it's when my heart rate is up. If I am feeling really tired, though, I just quit and do some yoga on deck to relax. As an athlete, I had already learned to listen to my body to prevent over-training and injuries; however, I sure am learning to listen to even more!
Thanks for your suggestions, advice, and support!