The Somogyi effect, also known as rebound hyperglycemia, is a period of high blood glucose following a period of low blood glucose. The elevated glucose values are most commonly seen in the morning.
The Somogyi effect arises from having extra insulin in the body before bedtime, either from not having a bedtime snack or from long-acting insulin injections. The extra insulin results in low blood glucose levels, and the body responds by releasing hormones that trigger the release of stored glucose. Often the body overcompensates for the low period, sending blood glucose levels above normal.