Adequate sleep is essential to wholesome health, especially brain function, as cells renewal and repair in the body are carried out during sleep. There should not be more than 8 hours of sleep as this can lead to malaise and lethargy, even so, less than 8 hours is considered inadequate for the production of serotonin. There’s a link between the level of serotonin in the body and depression. That is the main reason serotonin is important in brain function. The sleeping position is also important for restful sleep.