What else have you wondered?

Often roughly 90 minutes, but length varies between people and through the night. It is a guide, not an exact timer for setting an alarm.

All stages contribute to sleep. REM and non-REM have overlapping and complementary roles; a healthy night is not a contest to maximise one stage.

Yes. Vivid dreams are common in REM, but dreaming also happens in non-REM sleep. Dream recall does not reliably measure your stages.

Not necessarily. Brief waking can occur between cycles. If waking is frequent, prolonged or affects daily life, talk to a GP.

Sleep inertia is temporary reduced alertness after waking and can be stronger after deep sleep or insufficient sleep. It does not let you identify a sleep stage with certainty. Persistent daytime sleepiness deserves attention.

Consumer trackers estimate stages from signals such as movement and pulse, rather than directly measuring the brain activity used in a clinical sleep study. Use a chart as context, not a diagnosis.

Sleep pressure and body clock timing can pull in different directions. Stress, pain and other factors can also play a role; no single explanation fits everyone.

It can make you feel more alert by blocking some adenosine signalling. It does not replace sleep, and its effects can persist for hours.

No fixed number fits everyone. Most adults need around 7–9 hours. Sleep quality, regularity and how you function in the day matter too.

Speak to a GP if sleep problems persist and affect daily life. Breathing pauses, gasping in sleep or persistent daytime sleepiness also need assessment. Do not drive when sleepy.