Which of the following is a sign of hypoglycemia?

Cool, pale, diaphoretic skin is a sign of hypoglycemia, which is a condition characterized by abnormally low blood sugar levels. When individuals experience hypoglycemia, the body reacts to the low glucose levels by activating the sympathetic nervous system, often resulting in sweating and a cool or clammy sensation to the skin. This symptom helps differentiate hypoglycemia from other conditions since the body’s response includes an increase in perspiration.

In contrast, high blood sugar levels would indicate hyperglycemia, making it irrelevant to hypoglycemia. Difficulty breathing can occur in various medical emergencies but isn't specific to hypoglycemia; it may signify respiratory issues or other metabolic problems. Severe headache can be associated with multiple conditions, including stress or migraines, and isn't a direct or specific indicator of hypoglycemia. This makes cool, pale, diaphoretic skin the most accurate sign of hypoglycemia among the choices presented.