7.1 mi morning before work + 6.1 mi during lunch, all done easy. Feeling just a bit stronger today. Energy drain and fatigue feeling greatest between minutes 10 to 25. After that I'm good to go. Spoke with the doc about this today. Sounds like these feelings are common as body adjusts its oxygen levels. He emphasized electrolyte levels being maintained, which agrees with my conclusion. Heading back for full physical and blood tests (including thyroid and T levels).