Architecture of a Night

Your brain doesn't just switch off. It moves through a repeating cycle of about 90 minutes, again and again, all night.

Each cycle has two parts. First comes non-REM sleep, which deepens through three stages and handles tissue repair and memory storage. Then comes REM sleep, a separate state where the brain lights up almost like waking and vivid dreams appear.

The mix shifts as the night goes on. Early cycles are heavy on deep slow-wave sleep, the most physically restorative stage — this is when the body does most of its repair.

Later cycles tilt toward longer REM periods, which sort emotions and stitch ideas into creative connections. So cutting your night short doesn't trim sleep evenly. It mostly steals the REM you'd get in the final hours.