Everyone's heard that sleep comes in tidy 90-minute cycles — so just set your alarm to land between them and wake up refreshed, right? Except that's not quite how your brain works, and the alarm-hacking advice flooding wellness blogs may be leaving you more cognitively impaired than a late night ever would. This week, we dig into the actual architecture of sleep, what happens when you interrupt specific stages, and the one evidence-backed habit that matters more than any sleep calculator app.