Glycemia is the presence of sugar (glucose) in the blood. Hyperglycemia indicates excess glucose in the blood. Hypoglycemia refers to abnormally low presence of glucose in the blood.
Controlling blood glucose levels is the cornerstone of diabetes treatment. Using insulin injections and wisely consuming carbohydrates to maintain as stable and balanced blood glucose levels as possible keeps the body functioning properly and prevents long-term damage to vital organs. Monitoring your blood glucose to know whether the current levels are high or low is the only way to determine the appropriate treatment.
Source: The Healthy
See the images below for a more visual representation.