1. Hyperthyroidism (Grave's disease) causes an overactive thyroid gland and overproduction of thyroid hormones. Symptoms include weight loss, rapid heartbeat, nervousness, and eye bulging. Treatment includes anti-thyroid medications, radioactive iodine, or surgery. 2. Hypothyroidism (Myxedema) is an underactive thyroid gland. Symptoms are low energy, dry skin, and sensitivity to cold. Treatment is lifelong thyroid hormone replacement therapy. 3. Thyroid cancer is rare but can include papillary, follicular, medullary, or anaplastic forms. Treatment depends on cancer type and may involve surgery, radiation, or medications.