Symptoms of an overactive thyroid (hyperthyroidism) include: Anxiety, irritability, and nervousness Difficulty sleeping Weight loss An enlarged thyroid gland or goiter Muscle weakness and tremors Irregular menstrual periods or your menstrual cycle stopping Sensitivity to heat Vision problems or eye irritationSymptoms of an underactive thyroid (hypothyroidism) include: Fatigue (feeling tired) Weight gain Forgetfulness Irregular menstrual cycles Dry and coarse hair Hoarse voice Low tolerance to cold temperatures