Implantation dip (BBT charting)

Manda • Baby #1 March 10, 2016. Baby #2 November 1, 2017.
Anyone ever experienced an "implantation dip" on their chart and get a BFP? Around what DPO? Was it below your cover line? Did you temps go back up the very next day? How long after the dip before you tested +?
My bbt dipped below cover line this morning, dropping .5 from 97.9 to 97.4, at 8DPO. Hoping it's a good sign, but I'm not sure. Breast tenderness started late last night as well. 
Any help would be greatly appreciated! Good luck & baby dust!