National Sleep Foundation

Chapter 1: Normal Sleep

Normal Sleep

The need for sleep varies between individuals and across the life span as we age. Normally, adults sleep from about 8.25 hours per night; we spend one-quarter to one-third of our lives asleep1.  Sleep is not just the absence of wakefulness — rather, it is a complex and multi-dimensional state. Sleep influences all major systems of the body (see “The Physiology of Sleep”). And, this relationship is bi-directional, with many of body systems also influencing a person’s sleep. Sleep deprivation can drastically change an individual’s thinking and behavior and negatively impact their physical, mental, and emotional health.


  1. National Sleep Foundation (NSF), The Five Clusters of Sleep Patterns, Arlington: NSF, Available online at: