I do not trust, completely, the flat line of my CGMS… the measurement of interstitial fluid is always at least 15, maybe 20 - 25 minutes, behind my meter blood glucose. I can generally feel all lows, regardless of what the CGMS says… and my meter confirms anything I feel below 70. I got the CGMS to help spot the highs, and if I calibrate “right”; my MM CGMS is accurate at that., ( within the 20% range , which is + or - the blood glucose)
Maybe you are feeling something else other than a low reaction? I do not feel low at 80 unless it is a rapid drop from a high over 180 or so.