Traditional Chinese Medicine views almost all sleep disorders as stemming from either a deficiency in yin or from a surplus of qi in body organs, mainly the kidneys and heart. In the west, studies have shown that some insomnia may be due to a deficiency of endorphins (the body's own natural painkillers), and thus acupuncture is often a useful therapy. During acupuncture, patients tend to become drowsy or even fall asleep, possibly because of increased levels of central nervous system endorphins. Traditional Chinese Medicine also stresses the need to observe the body's natural daily cycle.