Are you experiencing sudden dips in glucose or odd patterns during the overnight hours that differ from your readings?
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If so, this is most likely caused by your sleep position. When added pressure is applied to your arm, the sensor receives less or more blood flow than usual which will affect the readings.

Since the sensor reads the glucose concentration in your interstitial fluid (right under the skin), this could vary if your arm is compressed.
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This is consistent with a study on CGMs that found nighttime drops were highly correlated with subjects lying on the sensor.

Steady decreases in blood glucose are also expected at night, especially during REM.
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