Your blood sugar has to be at least than 600mg/dl to have a risk of going into HONK. The average blood sugar in people with a diabetic coma is higher than 800mg/dl. It is not uncommon to see blood sugars higher than 1000mg/dl in a diabetic coma.
When your blood sugar gets this high, it means that the balancing act of drinking water and losing water in the urine has become unbalanced. Now you are losing more water than you are taking in. When this happens, it goes downhill fast.
As your blood sugars go higher, your blood becomes thick, like syrup. This draws water from your organs. The most significant effect happens on your brain. When the thick syrupy blood draws water from your brain, your brain shrinks. This triggers a series of symptoms that eventually lead to HONK.