Why do we need sleep?

Sleep is far from a passive shutdown; it is an active, essential process the body and brain cannot do without. During sleep the brain consolidates memories, transferring the day experiences from short-term to long-term storage and strengthening learning. A system called the glymphatic system becomes far more active during deep sleep, flushing out metabolic waste products, including proteins linked to Alzheimer disease, that build up while we are awake. The body also uses sleep to repair tissues, release growth hormone, regulate appetite and blood-sugar hormones, and support the immune system. Different stages, from light sleep to deep slow-wave sleep and REM sleep, each play distinct roles in recovery and mental function. Chronic sleep deprivation impairs concentration, mood, and immunity, and severe, prolonged lack of sleep can be dangerous, underscoring that sleep is a biological necessity rather than a luxury.