Early in the night, you may transition from lighter sleep stages (called N1 sleep) to deeper, slow-wave sleep (called
N2 and N3 sleep). REM sleep may appear, and it becomes more common during the latter part of the night, alternating with N2 sleep.
How Sleep Architecture Changes with Age
As we get older, both the amount and the quality of our sleep may change. Slow-wave sleep decreases and lighter N1 sleep increases.