In humans, metabolism only goes down ~35% at its very lowest point during deep sleep. In other phases of sleep, your metabolism is ~15% lower than during waking

In humans, metabolism only goes down ~35% at its very lowest point during deep sleep. In other phases of sleep, your metabolism is ~15% lower than during waking time. If sleep were for metabolic savings, it would be an incredibly inefficient way to go about it. In some senses, wakefulness may be thought of as neurotoxic and much of whats going on during sleep is centred around repairing the damage caused by being awake. For instance, the glial cells between your brain neurons shrink allowing your body to flush the beta amyloid from your brain with cerebral fluid. Beta-amyloid is a neurotoxic protein which causes Alzheimer's an is a byproduct of waking brain function. This explains the link between Alzheimer's and sleep deprivation. Sleep is also the phase where short-term memories are evaluated and either discarded or integrated into long-term memory. It's also essential for your immune health and cancer prevention. Your body produces dozens of cancer cells daily, but they're killed by your immune system. After only a single night's sleep deprivation, your amount of cancer-killing immune cells plummets. This is why shift work is now classified as carcinogenic in several countries. ____________________ Edit: Just on the topic of sleep being for energy savings, did you know that during hibernation (a state actually used for energy savings), bears will actually leave their hibernating state in order to sleep? I think that fact really showcases how important sleep is and should put to rest any notion that sleep is for energy savings.