Somogyi effect
A proposed rebound morning high after an overnight low; current evidence suggests this pattern is uncommon and remains debated.
The Somogyi effect (sometimes called rebound hyperglycemia) is the proposed idea that stress hormones after an overnight low can lead to a morning high. Modern glucose-monitoring studies find little support for it as a common explanation, so a high morning reading should not be assumed to prove an overnight low.
A short run of overnight checks or CGM data can show whether a low actually occurred. If it did, bring the pattern to your clinician, especially if you use insulin or another medicine that can lower glucose. Never adjust medicine from the morning number alone.