I have been having a heart rate of around 100 for 6 months now. I also had extreme insomnia and other symptoms like ringing in ears and shortness of breath. My doctor reffered me to cardiologist that found nothing so far. Only recently I noticed, that all of these symptoms comes only when I eat something salty/fatty that day (not sure, if it's only salt or also fat, because most of salty foods I eat have loads of fat), and I was eating foods like this all the time. The day I stopped eating salt, was the first time in those months I did not feel like in hell again, although heart rate was still higher that normal and I still felt anxiety. After a few days of not eating salt I ate a bag of crisps and that was the worst night that came after- I did not sleep until 6am and my heart was racing.
Maybe someone experienced something similar? Should I ask my doctor for kidney tests?