Are naps good or bad? It depends on the nap.

Power nap (10–20 min): light sleep only, wake refreshed. Full cycle (90 min): includes REM, wake at the natural cycle end without grogginess.

30–60 min naps risk waking from slow-wave sleep — that's the source of post-nap grogginess (sleep inertia).

Avoid napping. Daytime sleep reduces nighttime sleep pressure and worsens insomnia. Power through the afternoon to consolidate sleep at night.