Hi HartHen
It's part of the bodies automatic hormone response (dating way back to out cave dwelling family members I think...)
Essentially your liver 'fires up the burners' often around 5am stimulating a release of glucose into the bloodstream. (I think it's glucagon first, then glycogen then glucose but my biology's a bit shaky). In cave people this served to offer a little energy to help you catch woolly mammoths, but for some diabetics it can mean waking up high more often than not, even when no carbs have been consumed late in the evening before.
The effect varies from person to person, some have little or no DP, but for those with a big liver dump every morning it's very hard to get good breakfast time readings without a pump, or for T2s without some careful diet juggling and perhaps some late nite protein snacking.
The reverse is the Somogyi Effect where a diabetic (usually type 1) drops into an undetected hypo overnight and the liver kicks-in to emergency mode dumping glucose to bring levels up, often rebounding into hyperglycaemia. The snag with these two phenomena is that high BGs for a T1 can be caused by factors which require exactly opposite responses (either more, or less overnight insulin) and it can be very hard to work out which is which without a lot of overnight BG testing
M
Ooops posted at the same time as NRB 🙂