Why Do We Need Sleep? The reason why humans need sleep is not well understood although the most probable one appears to be that sleep is needed for rest, repair and restoration of the mind and body. It is also likely that memory and learning are consolidated during sleep. Much of what we do know comes from sleep deprivation experiments. When we do not get enough sleep, we become very sleepy, irritable and our mood is affected. Brain function is particularly disturbed with slowed mentation and difficulty thinking, and impaired performance in tasks requiring close attention. Many sleep experts agree that good sleep is essential to optimal intellectual performance, besides being an important time for resting the body. Enough good quality sleep on a regular basis helps us to achieve our full mental potential.