Robert Sapolsky, the Stanford neuroscientist famous for linking chronic stress to health breakdown, zeroes in on everyday behaviors that quietly spike your cortisol and trash your rest. The first culprit he names is replaying conversations in your head. That mental rerun keeps your brain locked in fight-or-flight mode long after any actual threat is gone. You’ll lie in bed dissecting a snarky email or rehearsing your comeback, and your nervous system stays on high alert—so falling asleep takes longer, REM cycles shorten, and you wake up with jittery energy and low mood. On Chris Williamson’s podcast, Sapolsky promised nine more routine habits with the same stealth effect on sleep, mood and hormonal balance. He argues that what feels like harmless overthinking actually prevents your body from resetting each night. That elevated baseline of stress hormones then seeps into your days, undermining focus, digestion and immunity. If you want to lower your all-day cortisol drip, he suggests catching this loop early—name it when it starts and shift your focus to something neutral, like breathing or an unrelated task. Keeping that pattern in check, he says, is one of the easiest ways to protect your health from the “silent killer” of chronic stress.