I was training for ironman triathlons, marathons, etc approx 10 years ago, when I became less and less tolerant to exercise, and tolerance has decreased at a reasonably steady rate since that time. I have adequate energy to maintain a demanding career, but now if I go for half hour run or similar I feel terrible for the next couple of days. symptoms include dizziness, nausea, sore eyes/headache, weakness, muscle tightness in neck, lack of concentration, etc. At work I now have very little tolerance for stress; similar symptoms apparent.
I am 50 yrs old with a lean build, and numerous blood tests, stress tests, etc do not indicate any abnormalties. Have been diagnosed with sleep apnea and have taken small dose of Welbutrin for mild anxiety for years. Diet is excellent; when symptoms first appeared was on a vegetarian diet which may not have included enough protein..;