Rhombencephalic sleep, also known as paradoxical sleep, is a term used to describe the sleep state of certain animals, particularly aquatic ones. During this phase, the brain exhibits slow waves similar to those seen in deep sleep, but the eyes move rapidly and dreaming occurs. Synonyms for rhombencephalic sleep include rapid eye movement (REM) sleep or desynchronized sleep. REM sleep is named after the observable rapid eye movements, while desynchronized sleep refers to the lack of synchronization in brain activity patterns. Regardless of the terminology used, this unique sleep stage plays a crucial role in memory consolidation, emotional processing, and overall sleep quality.