ABSTRACT
Sleep is essential for our health andwell-being and occupies approximately onethird of our existence. Before diagnostic tools were available, we characterized sleep based on behavioral criteria as a reversible state of consciousness with perceptual disengagement and relative insensitivity to the external environment accompanied by a posture with closed eyes and absent or only slight mobility (1). Because of its inactive nature, sleep was considered a passive state for many years. However, the development of polysomnography (PSG) provided physiological data revealing sleep as an active process crucial for maintaining normal body and hormonal functions including growth and tissue healing, learning and memory processing, and central nervous system repair (2).
