Which of the following is not a symptom of hyperthyroidism?

Fatigue is typically associated with conditions where there is a lack of energy or an overwhelming sense of tiredness, such as hypothyroidism rather than hyperthyroidism. In hyperthyroidism, the metabolism is accelerated, which usually leads to increased energy levels and hyperactivity rather than fatigue.

On the other hand, symptoms like exophthalmos, tachycardia, and tremor of extremities are classic signs of hyperthyroidism. Exophthalmos refers to the protrusion of the eyes, often observed in Graves' disease, which is a common form of hyperthyroidism. Tachycardia, or an increased heart rate, is also a hallmark of this condition due to the enhanced metabolic state. Additionally, tremors of the extremities occur due to increased sympathetic nervous system activity associated with the overproduction of thyroid hormones.

Therefore, fatigue does not align with the expected symptoms of hyperthyroidism, making it the correct answer to the question.