At what stage of sleep do most dreams occur?

REM sleep first occurs about 90 minutes after falling asleep. Your eyes move rapidly from side to side behind closed eyelids and brain wave activity becomes closer to that seen in wakefulness. Most dreaming occurs during REM sleep, although some can also occur in non-REM sleep. Your arm and leg muscles become temporarily paralyzed, which prevents you from acting out your dreams.

Source: National Institutes of Health