I just saw this and am experiencing the same exact thing as you. And same with you, I don’t think I suffer from anxiety, GERD or anything else that I can tell. Frankly, I thought I might be having heart issues so I got a complete work up and all came out fine. I was thinking maybe Long Haul Covid since my symptoms seemed to start when I had covid for the second time. But I work out, eat healthy, etc. and it does not really bother me when I work out or even sleep. It actually feels worse when I am sedentary. Very frustrating. Hopefully it does not get worse.