Sleep isn't one flat state — across a night the brain repeatedly sinks into deep NREM sleep and rises into dreaming REM. A chart of those stages over time is called a hypnogram. Press Next to walk through one whole night, or tap any part of the chart to jump there.
A whole night of sleep
Brain wavespress Next to begin
The red band is REM — dreaming sleep. Notice how deep sleep (Stage 3) dominates early in the night, while REM periods grow longer toward morning.
A night of sleeppress Next to begin the night
Cycles of about 90 minutesA typical night runs through 4–6 cycles, each roughly 90 minutes long. Every cycle descends through the NREM stages toward deep sleep and then climbs back into REM. Step through one night to see how the pattern shifts from dusk to dawn.