Humans spend one-third of their lives sleeping, yet the role of this phase of the circadian rhythm is not clear. Theories postulating the purpose of sleep include the restorative theory and the humeral theory. Both theories have identified weaknesses. What is known is that chronic disruption of sleep and/or sleep deprivation causes significant physiological and psychological symptoms. These include fatigue, lethargy and daytime somnolence accompanied by irritability, memory loss, decrease in judgment and paranoia. Obstructive sleep apnea (OSA) imposes another, more life-threatening dimension for the client.