A 53-year-old male presents with low-grade fever for 1 week, accompanied by anxiety, irritability, palpitations, and hyperhidrosis. Physical exam: T 37.6°C, P 100/min, palpable thyroid gland with a hard, tender nodule on the right side, no thrill or bruit; fine tremors of tongue and hands (+), ESR 78mm at 1st hour. The most likely diagnosis is: