Sleep isn’t one long, continuous state. It moves in cycles—quietly, repeatedly—throughout the night. About every 90 minutes, your body shifts between different stages: Light sleep (where you drift in and out) Deep sleep (where your body repairs itself) And REM sleep—the stage where your mind becomes active again Each cycle builds on the last. And as the night goes on, something interesting happens: Your REM sleep gets longer. That means the early part of the night is more phy