You're in your late 30s or early 40s. You feel anxious in a way you never used to. Your sleep is a mess. You're exhausted, foggy, and your period has gotten unpredictable — and somewhere in the back of your mind you're wondering if something is wrong with you. Here's what almost no one tells women in time: this might be perimenopause, and it can start a decade before the hot flashes everyone warned you about.