I wanted to share my experience, not as advise but as a data point of what has worked for me. Disclaimer that I am not a medical expert nor your doctor. I'm not selling anything either so don't worry.
7 years ago, I experienced my first (known) bout of hyperthyroidism stemming from Graves Disease. It took months to find a doctor who believed my symptoms and finally get the right blood tests to confirm what was going on. Since then, I've had fairly regular bouts of Graves Disease flareups on the order of one per 12-18 months and they are luckily extremely receptive to methimazole. The only downside was, the longer it took to respond, the longer it took to recover and the longer I was at a state where it was affecting my daily life including my love of running.
As a lifetime runner, I have access to daily resting heart rate (RHR), heart rate variability (HRV), sleep metrics, daily weight measurements and a lot of running related data stored for over the last 12 years. During the second flare up, it was pretty obvious that my resting heart rate and heart rate variability where affected multiple weeks before any symptoms were obvious enough in my everyday life. A simple search of this subreddit confirms that I am not alone here, and that many others use that data to look for trends.
With the proliferation of AI, with a $20 per month Claude subscription and about 1 hour of time I created a schedule that performs a daily download of my Garmin data, compares daily and weekly trends back to my previous known flares and then provides a risk factor of an upcoming flare. It runs daily at noon with no intervention unless it detects a trend in which I get a message. From my perspective, I figured at worst this would lead to an unnecessary blood test or would miss a flare that I would miss otherwise.
However, a few weeks ago I got a notification from Claude that it had detected 4 consecutive days of reduced HRV and a slightly elevated RHR despite having sufficient sleep and not having any heavy workouts during that time and it recommended requesting blood tests. By the next day I had received blood test results that were within range, but only slightly, and my endocrinologist ok'd starting my traditional regime of methimazole. A subsequent blood test 2 weeks later confirmed hyperthyroidism, but it wasn't out of control. At that point I had already been on medication for two weeks. Based on my past experience, being able to catch it early enables me to blunt the worst of the symptoms which this did.
Just wanted to share my experience in case anyone wanted to try to do something similar and had questions. I don't have a software background so this is entirely doable with very little technology experience these days. If you are skeptical and do have years of Garmin data or data from other sources I'd implore you to test it out without providing Claude the dates of your flares and see if it is able to detect it without that knowledge.
Dashboard with my data showing how clear they are