Sleep stages are distinct categories
NON-REM SLEEP
N1
Transition from
wakefulness.
N2
Asleep; distinct
from deep sleep.
N3
Deep / slow-wave
sleep.
REM
Active brain;
rapid eye movements.
Across the night
Earlier: usually more N3
Later: usually more REM
Stages recur across the night, with individual variation.
These boxes show categories, not duration or a personal sleep trace.
Conceptual diagram • not measured data