Last night I woke up shaking, heart racing, slightly nauseous…and my Dex reads 90. I scarf down two glucose tabs, wobble into the bathroom to wash my hands, and check my BG with a fingerstick (which was hard to do ‘cos my hands were shaking so much). Fingerstick says…78. What?? Second test five minutes later says 62!! I felt the way I do when I’ve dropped to the high 40s but the Dex kept reading low 80s. Twenty minutes later the symptoms were subsiding and in 40 minutes a fingerstick and the Dex both showed in the 90s. Very, very weird and a bit scary!!
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This sounds like something I have talked to @LarissaW about. The “Ghost Low”. Where you feel it before it shows on either BG test or CGM.
It happens frequently to me. I can be flat-lining on both BG tests and CGM, but I still feel a low. I keep testing and it does not show it, but then 15-20 minutes later, I plummet.
Happened the other night, several BG tests in the 70-80 range, I felt horrible, and then 20 minutes later my test was in the 30’s.
Don’t take it as being scary, take it as just a testament to your awareness.
Look at it this way, CL. If you are really skilled, you know it before both CGM and BG test. 
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That phrase is totally spot on!! I guess it’s reassuring to know that others experience this!? 
LOL! Shaking the way I was a real give-away! 
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Dexcom will miss lows pretty frequently for me if I correct the low before dexcom has even picked it up! I don’t think I’ve had any ghost lows like you and @Eric described, but maybe it’s just that I haven’t noticed before or that if I’m feeling low sometimes I’ll treat it and don’t get around to testing for a few minutes after (from rushing around or needing to wash my hands!)
Moving forward I’ll keep an eye out tho - go ghost hunting !
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My Dexcom has had this problem a few times, but I usually have the opposite problem. The alarm has frequently occurred during the night with a number in the 50-70 range, and a fingerstick showed a number in the 80-100 range. To keep the alarm from continuing additional times, I turn it off, and set my clock to wake me up an hour later. Then I can turn the Dexcom alarm back on again.
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I had another one of these “ghost lows” last night and felt really weird for a while, even though I didn’t drop really low, just dropped faster than the sensor could register. I usually try to wear a sensor at least 2 weeks but have found this one to be very unreliable (data drop-outs, false lows, etc.) and am going to change it out today.
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My sensor never lasts more than 10 days. Usually by day 9 it is already starting to see noise, a good hint that it will soon need replacement !
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