Hyperglycaemia
This is when your blood sugar levels are too high and is generally what alerts your medical practitioner to the fact that you have diabetes.
However it can also occur after you have been diagnosed if:-
1. You take insufficient insulin or oral medications.
2. You eat the wrong foods eg. to many carbohydrates.
3. You develop an illness (Even the common cold) that can effect your blood sugar levels.
4.Your exercise levels change.
For example if someone who does heavy manual labour sustains an injury that results in them being unable to do their normal level of work.
Treatment
Is obviously to do what is necessary to bring the blood sugars down.
This may involve adjusting medication levels, a change in diet and finding alternative means of exercise. Sometimes hospitalisation is required until BG levels are stable.