Hyperthyroidism is a type of thyroid disorder. It is defined as having too much thyroid hormone and is sometimes called "overactive thyroid." It involves acceleration of body functions, and symptoms include increased heart rate, anxiety, weight loss, difficulty sleeping, tremors in the hands, weakness, and sometimes diarrhea. There may be puffiness around the eyes, dryness, irritation, and, in some cases, bulging of the eyes. The affected person may experience light sensitivity and visual disturbances. Because the eyes may not move normally, the person may appear to be staring.
For further detail, including information on tests, see the Thyroid Diseases article.