Sleep stages are organized by cycles across the night. When you lie down to sleep, you will first transition from relaxed wakefulness to NREM stages 1 and 2 (light sleep) to NREM stage 3 (slow wave or deep sleep). You will then transition through stage 2 to REM sleep, completing the first cycle. Each cycle is between 60-120 minutes long, and 4 -6 such cycles will be seen throughout the night.

Slow wave sleep is seen prominently in the first third of the night. Similarly, REM sleep becomes progressively longer during the final third of the night. Therefore, your sleep is deeper in the first third of the night and your dreams are more prominent in the final third of night.