Get that thyroid thing rechecked. Doctors may say "It's within normal limits" but that doesn't mean it's right for you.
Back in early summer I got some bad advice from a nurse practitioner at my health network's geriatric clinic (yeah, at 60 I really dislike that whole concept). She told me to quit taking thyroid meds because my thyroid panel showed normal. Made no sense to me but I followed her instructions.
Huge, mistake. Within a few weeks I was wiped out, barely enough energy to get out of bed. Went to urgent care, the doc redid the thyroid panel. It was just barely within normal limits, but she said that doesn't mean it's normal for me. Started me back on levothyroxine. Took about three weeks before I began to feel better. Now it's six weeks and I'm starting to get back to normal.
But my heart rate is still all over the place. That's typical of both Hashimoto's (my first diagnosis about 17 years ago) and Graves diseases, and some endocrinologists say some patients flip-flop between Hashimoto's (hypo-thyroidism) and Graves (hyper), which makes diagnosis and treatment even trickier. My resting pulse can vary from 60-100. My low effort HR is 120, moderate is 140, high sustainable effort is 160, and maxed out for HIIT sprints of 15-60 seconds is 170-175. That's as high as I can crank up my heart rate.
The weird thing is my BP will drop to normal or even a bit low immediately after a workout, as low as 80/50 before stabilizing at 110-120/60-70. But my heart rate will remain 90-100 for an hour or longer after a workout. It takes hours before it drops to 70 or so. Again, a symptom of a wonky thyroid.
So don't go just by TSH and T4 panels that show you're within "normal" limits. It may not be normal or optimal for you.
Diet and rest are bigger factors as we get older. I felt great Wednesday morning and early afternoon, then crashed suddenly on the train ride home from the doctor's appointment. I'd planned on a ride when I got home but napped instead. Woke up after 10 pm, felt lousy, ate "breakfast" and now I feel fine again. So I'm going for a bike ride, even though it's 3 a.m.
Good reminder that I'm not 20 anymore and need to eat more regularly, even when I'm not hungry, and rest even when I think I'm not tired.
I got a second opinion this week and the doc said the same thing -- have the thyroid removed, most of it or all, depending on what they find in surgery and post-surgical section biopsy. So I'll be on thyroid meds the rest of my life. Fine with me, as long as I can keep riding and working out within reasonable expectations.