Just as an aside, I own a BP monitor. A few years ago, my doctor made changes to my heart/BP meds and wanted me to monitor and note readings to make sure we were reaching the desired results. The instructions were to place the cuff on your arm and find a place to sit and relax. I was to chill for 5 minutes and then take three readings. The lowest of which I was to notate. While none of my readings were high, it was always the case the 3rd reading was the lowest. It makes total sense the same would happen with anxiety sufferers as they calm down.
Positive thoughts