Slow-Wave Sleep
The deepest sleep stage. It builds your brain and body while you're offline. Protect it.
Grounded in the research on Slow-wave sleep (https://en.wikipedia.org/wiki/Slow-wave_sleep)
Know what it actually is
Slow-wave sleep (SWS) is stage N3 of NREM sleep, the deepest stage, formerly split into stages 3 and 4. Named for delta waves on EEG: high-amplitude (>75 microvolts), low-frequency (0.5-4 Hz) brain activity. This is the hardest stage to wake from, and if you do get woken you'll be groggy and disoriented (sleep inertia). It is NOT REM, that's the dream stage. SWS is the offline-repair stage.
Get the front-loading timing right
SWS is not spread evenly across the night. It's dominant in the first third, your deepest N3 happens in the first 1-2 sleep cycles, then shrinks each cycle while REM grows toward morning. Translation: the first ~3 hours after you fall asleep carry most of your slow-wave sleep. Go to bed late or get a fragmented start and you lose the deep stuff disproportionately. It declines hard with age too, peak in childhood, way less by 60.