Sleep stages decoded in 5 fast facts

N2 is the stage with sleep spindles and K-complexes, often 10 to 25 minutes in the first cycle.

N3 is the deepest non-REM sleep, or slow-wave sleep, and is most concentrated early at night.

REM brings vivid dreaming, rapid eye movements, and temporary muscle atonia, usually starting about 90 minutes after sleep begins.

Micro-arousals are brief wake intrusions during sleep, commonly lasting about 3 to 15 seconds.