I've written often enough about wearing a fitness tracker, and I've been pretty happy with my Garmin Venu. The device has a feature called "body battery" which uses heart-rate variability and other measures to estimate how much energy you have. I've actually found it a reliable measure, in that when I check in on how I feel and then compare that to my body battery score, it seems right.
For instance, I would say this chart is a pretty decent proxy of how I've felt for the past week:
My symptoms hit Thursday night, were worst on Friday (I took a rapid test when I woke up Friday), but by this afternoon almost non-existent. In fact, I feel better today than I have in a while,
I've found the body battery metric useful in other ways, too, mainly in timing activities and socializing. That Scotch right before bed, even if it's the only drink I have all day? There's a cost. I've also learned that as much as I enjoy traveling, being in a moving vehicle is draining.
I've got a stressful week coming up, followed by a couple of very-low-stress weeks. I'm interested to see how I manage my energy levels with this metric.