Feeling jittery as the week kicks off isn’t just a mood—it leaves a biochemical footprint. Researchers tracked thousands of older adults and found those who dread Mondays carry elevated cortisol in their hair for months, a stress echo that may help explain the well-known Monday heart-attack spike. Even retirees aren’t spared, hinting that society’s calendar, not the workplace alone, wires Monday anxiety deep into the HPA axis and, ultimately, cardiovascular risk.