Sleep is not one flat state. Across a night, the brain sinks into deep NREM sleep again and again, then rises into dreaming REM. A chart of these stages over time is called a hypnogram. Press Next to walk through one whole night, or tap the chart to jump. Then set an alarm and see what it does to your sleep.
A whole night of sleep
Brain wavespress Next to begin
The red band is REM, the dreaming stage. Notice how deep sleep (Stage 3) fills the early night, while REM periods get longer toward morning.
Set an alarm
REM you got
Deep sleep you got
A night of sleeppress Next to begin the night
Cycles of about 90 minutesA typical night runs through 4 to 6 cycles. Each is roughly 90 minutes long. Every cycle goes down through the NREM stages toward deep sleep and then climbs back up into REM. Step through one night to see how the pattern shifts from dusk to dawn.