REM (Rapid Eye Movement) sleep is the phase of sleep most strongly associated with vivid dreaming. During REM, brain activity becomes more similar to waking consciousness — the brain is highly active, the eyes move rapidly beneath the eyelids, and the body experiences temporary muscle paralysis, preventing you from physically acting out your dreams. This stage typically begins about 90 minutes after falling asleep and recurs several times throughout the night, with each REM phase lasting longer than the previous one. REM sleep is also believed to play a critical role in memory consolidation, emotional regulation, and cognitive function. While dreams can occasionally occur in non-REM stages, REM is when the most intense, story-like dreams take place. Disruptions in REM sleep can lead to fatigue, difficulty concentrating, and mood swings, highlighting just how essential this phase is to restorative rest and mental clarity.