High levels of thyroid indicate hyperthyroidism, a condition whereby the thyroid gland produces too much thyroid hormone, according to WebMD. The most common cause of this is Grave's disease, which tends to be hereditary.
Hyperthyroidism occurs when the thyroid gland, situated in the neck, produces too much thyroxine, which is a hormone that controls the body's metabolic rate, according to WebMD. Too much of this hormone increases the metabolic rate.
Other symptoms related to an overactive thyroid include shortness of breath, frequent mood swings, feeling tired and bloodshot eyes. A physician may order a blood test to measure the amount of thyroid hormone in the body if he suspects hyperthyroidism, states NHS Choices.