This is from a diabetes web site:
What is the Somogyi effect?
During periods of hypoglycemia, the body releases hormones which cause a chain reaction to release stored glucose. The end result is that the glucose level can swing too high in the other direction, causing hyperglycemia.
How can you test for the Somogyi effect?
This is the fun part. Set your alarm and wake up between 2 and 3 a.m. and test your blood glucose. Low blood glucose levels could signify the Somogyi effect is in action.
What can I do to correct the Somogyi effect?
Have a snack with protein before bedtime, like a piece of toast with peanut butter, or some cottage cheese, or yogurt, or some nuts and small piece of cheese.
Go to bed with a glucose level slightly higher than usual.
Ask your doctor about having the CGMS test (see above description).
What is the dawn phenomenon?
How can I treat the high fasting glucose readings caused by the dawn phenomenon?
Several options are worth considering:
Exercise later in the day, which may have more of a glucose-lowering effect in the night.
Talk with your doctor about a possible medication adjustment to control the higher fasting readings.
Limit bedtime carbohydrates and try more of a protein/fat type of snack (nuts, peanut butter, cheese, or meat).