Twice now in a week, I've been on a run and my HR has plummeted (I'm usually around 145 bpm, and it drops below 110). I tried adjusting my strap (Garmin Dual-HRM) and today it was certainly not an issue of being dry. There were 5 days and two activities in-between this happening, both with seemingly good data. Both times, the temperature was 15–20ºC—I've run in hotter and colder without issues. Any tips are appreciated.