When the thyroid gland produces an excess of thyroid hormones, hyperthyroidism occurs. The thyroid gland is a butterfly-shaped gland located in front of your neck and plays an important role in body functions.

The symptoms of hyperthyroidism include
Mood swings,
Nervousness
Irritability
Irregular and fast heartbeat
Fatigue
Muscle weakness
Inability to tolerate heat
Shaky hands
Frequent bowel movements
Difficulty in sleeping
Swelling around the front part of the neck

The following are the causes of hyperthyroidism:
Grave’s disease (immune system attacks the thyroid gland and makes it produce more thyroid hormones)
Inflammation of the thyroid gland
Nodules or abnormal growth in the thyroid gland,
Excess intake of iodine
Excess intake of thyroid hormone medicine
Tumour in the pituitary gland.

Hyperthyroidism is diagnosed based on the symptoms, blood tests and scans.
Blood tests are done to check levels of thyroid-stimulating hormone (TSH), triiodothyronine (T3) and thyroxine (T4). Low TSH levels and high T3 and T4 levels suggest hyperthyroidism. If necessary, your doctor may order a radioactive scan of the thyroid gland to examine the nodules or growth present at the gland.

Yes, it is possible to treat hyperthyroidism. The treatment includes the following:
Medication that stops the excess production of the hormone
Low dose radiation that partially damages the thyroid gland so that it does not produce excess hormones
Partial or complete surgical removal of the thyroid gland