A 17-year-old baseball player is brought to the emergency department by EMS. His temperature is 38.5°C (101.3°F) BP is 80/65 mm Hg, and pulse is 100 beats/min. He says he is dizzy when he stands, feels weak, and has heart palpitations and a dry mouth. He collapsed on the ball field while playing in 100+°F heat. What might the nurse suspect is wrong with this patient?