Cortisol is a neurohormone released after a cascade response to stressors that begins in the hypothalamus, moves to the pituitary gland, and then to the adrenals, which secrete cortisol into the bloodstream as the final stage in this cascade. Cortisol affects many physiological functions, including vital anti‐inflammatory and immunosuppressive actions, as well as metabolism and homeostasis. Consequently, a basal concentration of cortisol is required at all times but may become immediately elevated in response to physical or mental stressors, usually returning to basal levels later. Underneath this immediate response to stressors, cortisol displays a diurnal variation so that concentrations are at their apex about 45 min after waking in the morning and decrease to their nadir in the early evening, a process referred to as the diurnal fluctuation in cortisol. However, this variation may become dysregulated by chronic stress and instead become consistently elevated, resulting in hypercortisolemia, which is characterized by an ongoing elevated concentration of cortisol in the bloodstream that is associated with pain, fatigue, increased risk of heart disease, and the symptoms of anxiety, muscle wastage, and hyperglycemia.