Sleep remains one of biology's great mysteries. We spend roughly a third of our lives asleep, yet scientists are still uncovering why sleep is essential and what happens during those unconscious hours.
Sleep consists of cycles alternating between REM (rapid eye movement) and non-REM stages. Non-REM sleep progresses through lighter to deeper stages, with the deepest phase crucial for physical restoration and immune function.
REM sleep, when most dreaming occurs, appears essential for memory consolidation and emotional processing. The brain is highly active during REM, yet the body is temporarily paralyzed—a mechanism that prevents us from acting out our dreams.