There is more than one kind of quiet.
Non-REM includes three stages: N1, N2 and N3. It makes up much of the night — but “non-REM” does not mean “all deep sleep”.
Follow the change in depth.
N1 · Drifting inThe transition from wakefulness
This is light sleep. You are usually easy to wake and may feel as though you were only dozing.
N2 · Settling into sleepA substantial part of the night
Brain activity shows characteristic patterns used to identify this stage. Heart rate slows and body temperature falls. Light sleep is a normal, useful part of a night.
N3 · Deep sleepAlso called slow-wave sleep
Slow brain waves characterise this stage, and you are harder to wake. Deep sleep contributes to recovery and memory. Sleep more broadly supports tissue repair, hormone regulation and immune function.
A tracker labels much of a night as “light sleep”. Does that automatically mean the sleep was wasted?
Read the explanation
N1 and N2 are part of the normal pattern, not failed attempts at deep sleep. A consumer device’s stage labels are estimates, so a chart alone is not a diagnosis.
What changes with age?
Deep sleep tends to decrease as we get older, and sleep may become lighter. That change does not automatically mean a sleep disorder.
If sleep difficulties persist and affect how you function, discuss them with a GP. Do not dismiss ongoing exhaustion simply as getting older.