Sleep: Its nature and mechanism in Avicenna's medicine and psychology

Sleep is a fundamental necessity for humans and other living beings. Throughout history, many thinkers have sought to understand its complexities. Avicenna, in his works, elucidates the nature and mechanism of sleep from two angles: "sleeping," as an essential process for sentient beings, and "dreams," which reflect the effects of sleep on human life and health. This article explores sleep through Avicenna's lens, examining its philosophical, psychological, and medical foundations. It begins with a definition of sleep, followed by an analysis of its causes, manifestations, and types, including natural, unnatural, and artificial. The findings indicate that Avicenna was a pioneer in studying altered states of perception within the imagination, showcasing his understanding of hypnotic sleep and its therapeutic applications for disorders like melancholy.