Which of the following is a sign of hypoglycemia?

Pale skin is associated with hypoglycemia due to the body's physiological response to low blood sugar levels. When glucose levels drop, the body attempts to compensate by releasing adrenaline (epinephrine), which can cause peripheral vasoconstriction, leading to a pallor in the skin. Furthermore, the sudden lack of glucose can also trigger various symptoms related to the brain's energy deficit, including confusion and weakness, and the body's stress response may manifest as changes in skin coloration.

Other choices do not typically indicate hypoglycemia. Rapid weight gain is more indicative of an energy surplus rather than a deficit. Thirst and dehydration are often associated with hyperglycemia or diabetes mellitus rather than hypoglycemia. Severe headache can occur with many conditions but is not a specific symptom of hypoglycemia. The specific signs of hypoglycemia focus on neurological manifestations and autonomic symptoms, such as paleness, sweating, or trembling.