Final answer:
The correct term for insufficient sugar in the blood is hypoglycemia, which is a condition characterized by a dangerously low level of blood glucose, affecting brain function and energy levels.
Step-by-step explanation:
The term that means insufficient sugar in the blood is D. hypoglycemia. Hypoglycemia refers to a condition where there is a low blood sugar level. This can be a dangerous condition because glucose is the primary source of energy for the brain and a lack of glucose can lead to symptoms like confusion, weakness, and in severe cases, seizures or unconsciousness. In contrast, hyperglycemia indicates a high blood sugar level, which is often associated with diabetes mellitus. Other terms, such as hypercalcemia and hyponatremia, indicate abnormally high levels of calcium and lower-than-normal levels of sodium in the blood, respectively, and are not directly related to blood sugar levels.