Diabetic coma = hyperglycaemia. However, someone with diabetes can, in theory, go into a coma, either hypoglycaemia or hyperglycaemia. In practice, I suspect that people with diabetes who have never been anywhere near unconsciousness / coma, like me, are probably in the majority, particularly if you ignore the period immediately before diagnosis of type 1. Hypoglycaemia is basically an overdose of insulin (or some oral medications, but not metformin - although it is possible to become hypoglycaemic on metformin - see next phrase), but it is possible for people to become hypoglycaemic after long periods of physical exertion without adequate carbohydrate intake eg athletes in extreme training / races, starvation without exertion etc.