The ATA (American Thyroid Association) estimates that more than half of thyroid conditions remain undiagnosed.
Hypothyroidism is more common, and this is when the gland is not active enough. This condition can make you feel sluggish and cause you to gain weight. It can also make you feel tired and have trouble with colder temperatures. On the other hand, if you have hyperthyroidism, it means your thyroid is too active. It is producing too much hormone.
Symptoms of this condition include weight loss, a speedy heart rate, and a sensitivity to hotter temperatures. There are many causes for both conditions. Treatment involves trying to reset your body's metabolism to a normal rate.
The most common example of hyperthyroidism is Graves' disease. According to MayoClinic.com, the attack of the immune system on the thyroid gland causes the disease to develop. Extra hormones are released during the attack increase the metabolism.
https://www.empowher.com/thyroid-conditions/content/thyroid-conditions-and-their-effects-you