Sleep-wake disorders are characterized by issues with sleep quality, timing, and quantity, which cause daytime disturbance and impairment in functioning. Sleep disorders are associated with both physical and emotional issues, and often co-occur with conditions like depression, anxiety, or cognitive disorders. There are many forms of sleep-wake disorders, the most common one being insomnia. Others include obstructive sleep apnea, parasomnias, narcolepsy, and restless leg syndrome. These are important to attend to, as sleep disorders may contribute to or intensify medical and mental illnesses, and may be indicative of other mental illnesses.