The most characteristic and most frequently reported symptoms of Hashimoto's disease include constant fatigue and sleepiness. Fatigue experienced with the co-occurrence of Hashimoto's disease may not be related to lack of sleep or intense physical or mental effort.
Decreased muscle metabolism, slower heart rate, and slower brain function lead to reduced exercise capacity. It is because thyroid hormones (thyroxine and triiodothyronine), whose production and secretion to the blood drops in this disease, are responsible for regulating metabolism. With a deficiency of hormones, the metabolic rate can decrease by up to 30%.
Additionally, there is a link between hypothyroidism and depression, with bad mood and depressive states being able to occur even when the thyroid secretory function is normal – physical changes have been found, but the concentration of hormones in the blood is normal.
