The dawn phenomenon. This is the end result of a combination of natural body changes that happen while you’re asleep. Between 3 a.m. and 8 a.m., your body starts to increase the amounts of certain hormones that work against insulin's action to drop blood sugar levels. They enter your system just as your bedtimeinsulin is wearing out and sugar levels rise.
The Somogyi effect. Named after the doctor who first wrote about it, this is also called "rebound hyperglycemia." The term refers to pattern of high morning sugars preceded by an episode of low blood sugar, or hypoglycemia (usually with no symptoms, but night sweats can be a sign). Your blood sugar may drop too low in the middle of the night, so your body counters by releasing hormones to raise it. This could happen if you took too much insulin earlier or if you didn’t have enough of a bedtime snack.
To learn the reason for your high morning blood sugar, your doctor will likely ask you to check your levels between 2 a.m. and 3 a.m. for several nights in a row.
If it’s consistently low during this time, the Somogyi effect is likely to blame. If it’s normal or high during this time period, the dawn phenomenon is more likely at fault.