Hyperthyroidism is a disorder characterized by excessive thyroid hormone production, leading to symptoms like nervousness, weight loss, and a rapid heartbeat. Diagnosis involves medical history, physical exams, and blood tests to confirm hormone levels, while treatment options include medications, radioactive iodine therapy, and surgery, depending on the cause and severity. Common causes include Graves' disease, thyroid nodules, and thyroiditis, with women and older adults being more frequently affected.