I have been using StressWatch for about a month, and it's a helpful free tool...but I was noticing a small discrepancy between how my body feels (if I really pay attention) and the ratings on StressWatch. Reading up more, I realized that StressWatch is based on intermittent readings that might not necessarily align to the same point in time. I researched to see what other alternative might be available and I found one that I really like.
https://www.makevisible.com
This tool/app was designed specifically for Long COVID patients and pairs with a Polar HR monitor that takes continuous readings. The information I have been getting from this is SHOCKING. I'm learning a lot about my body, PEM and how little it takes to over-exert...which explains why I have crashes when I can't determine the cause. I've found it to be very helpful so far!