Even today, the real importance and science of sleep is not fully understood. We do understand that sleep is a building process for the body, restoring the energy of the body and mind. During sleep is when our body also repairs damage and rebuilds muscle tissue. The body also secretes important growth hormones during sleep, which is important throughout adulthood. A number of breakthroughs have occurred in recent years shedding light on why we need sleep and what it does for the body and mind.
There are actually a number of theories about why we need sleep. An early theory is the inactivity theory, which states that inactivity during the night is a natural adaption that keeps animals out of danger during times when they are most likely to be hurt. The energy conservation theory, on the other hand, suggests that sleep conserves important resources and allows animals to remain competitive. Science does show that our metabolism does reduce up to 10% during sleep.
Finally, the brain plasticity theory is based on science around brain plasticity, which is still not fully understood. Brain plasticity means that our brains are constantly changing, processing and storing new information. We know that sleep is important for developing children and infants, who need much more sleep than adults and spend 50% of their sleep in the REM stage, during which dreams occur.
Sleep has many affects on the brain, allowing it to shut down and repair neurons and synapses that gradually break down. Sleep may also be used to improve synapic connections and allow them to restore after a day of activity. During sleep the brain also reorganizes information and processes fresh data to organize and archive our memories. The brain also has the ability to filter events and restore glycogen levels.
It's easy to see why we need sleep by studying what happens to the body when we don't get enough sleep. When we don't get adequate sleep it results in in reduced mental capacities, impaired memories, hallucinations and extreme moodiness and emotional problems. People who have chronic sleep problems experience reduced performance at work, an inability to concentrate, slower reaction times and behavioral problems. They're also more accident prone because motor skills are reduced without proper sleep.
While we don't understand sleep completely, we do know what happens to the brain while we sleep. It spends this important resting phase rejuventating and restoring connections and repairing damage. It reorganizes information and helps us lock in memories from the day. For infants and small children, sleep is important to lock in new information and build new pathways in the brain. The body also uses sleep to heal and repair damage in the body, including muscle tissue and skin. Without enough sleep you'll first experience moodiness and trouble concentrating, although this will gradually get worse. After a few days without sleep it's not uncommon to experience hallucinations, tripping, slow reactions and mood swings. Going too long without sleep can even be fatal, further emphasizing why we need sleep to function.