Cortisol, commonly known as the “stress hormone,” is a chemical made in the brain that plays a role in our stress response, metabolism, and immune system. Cortisol levels in the body peak when you wake up in the morning and decrease to their lowest point in the evening, playing a key role in the body’s sleep-wake cycle. The morning increase in cortisol levels, known as the cortisol awakening response, may contribute to feelings of anxiety in the morning after you wake up.