“Hyperthyroidism means that your thyroid gland is making too much thyroid hormone. You may also hear the term thyrotoxicosis. This also means there is too much thyroid hormone in your body.  Everyone is different and you may not have all the symptoms. Symptoms can start suddenly or come on slowly over time.  Hyperthyroidism can be caused by an autoimmune condition (Graves’ disease), inflammation of the thyroid (thyroiditis), or due to thyroid nodules making too much thyroid hormone (hot nodule or toxic multinodular goiter).”

American Thyroid Association (Hyperthyroidism | American Thyroid Association)