The underlying possible mechanisms may include insomnia-mediated dysregulation of the hypothalamo-pituitary-adrenal (HPA) axis due to increased secretion of cortisol, altered levels of hormones (orexins, ghrelin, serotonin, melatonin), and stress-related metabolic alterations with its resultant impact on the sympathetic system [215]. This evidence concerns the gene HCRT and insomnia.