The thyroid gland (located in the throat) and adrenals (located on the tops of the kidneys) work together. The adrenals are responsible for making and releasing adrenaline. Adrenaline acts on the hypothalamus which stimulates the pituitary to release thyroid stimulating hormone (TSH), which then activates the thyroid and so begins the cascade for thyroid hormone production. There is a feedback mechanism in which the thyroid hormone acts back upon the hypothalamus to further control the amount of thyroid hormone in the body.
Because thyroid and adrenals are dependent on each other, if you don't have enough adrenaline, then you won't have enough thyroid hormone. In order to gain clarity on how the adrenals are working, blood pressure can be examined to indicate if and how the adrenals can be supported.
Thyroid hormone is important because it controls mitochondria and therefore the production of ATP (energy) in cells. If your cells are not producing the energy they need, this will drain the whole body's energy system. To understand if your thyroid is working properly, FreeT3 needs to be measured. With this number a protocol for taking dessicated thyroid hormone can be constructed and monitored.