Well, I'm glad I was able to contribute to your peace of mind on the subject. Fear of the unknown is quite possibly the biggest impediment to fasting for a lot of ppl, or else causes them to cut it short.
I once went thru a phase of a thumping heart beat that took several days to calm down - experienced from days 7-11, finally getting back to normal on day 12. I thought my heart was going to explode, and came within a whisker of breaking because of it. Glad I didn't though.
When you know the possible causes, and how often it is reported by fasters, it suddenly seems a lot less frightening.
Well done on yours btw - that's good going, & I wish you the best for your fasting goals.