Which of the following symptoms would suggest hypoglycemia in a patient?

The presence of tachycardia in a patient suggests hypoglycemia, which is a condition characterized by an abnormally low blood sugar level. When blood sugar drops, the body reacts by releasing hormones like adrenaline (epinephrine), which is responsible for increasing the heart rate (tachycardia). This physiological response is part of the body's mechanism to help mobilize energy stores and restore normal glucose levels.

While fever, hyperthermia, and severe headache can be symptoms of various medical conditions, they are not specific indicators of hypoglycemia. Fever and hyperthermia typically indicate infection or inflammatory responses, whereas a severe headache could point to a multitude of issues, such as migraines or tension-type headaches. Therefore, tachycardia is the most direct symptom linked to the body's response to low blood sugar, making it the correct choice when assessing for hypoglycemia.