The people suffering from insomnia disorders complain of difficulty in initiating or maintaining sleep or of not feeling rested after sleeping adequate amount of time. Insomnia is associated with acute and chronic medical problems and may be a significant difficulty in those engaged in shift work and other economic activities that are out of phase with societies' normal circadian rhythm. Insomnia is related to depression, stress, environmental disruption and anxiety and there is evidence that it is on the rise.
Insomnia is experienced by virtually everyone in society, at some time or other in their lives. An estimated 35% of Europeans have some degree of insomnia, and 10% suffer acutely.
An estimated 60 million adult Americans may have a severe problem with insomnia: 51 percent had symptoms of insomnia a few nights a week; 29 percent experience insomnia every night or almost every night; 32 percent are awake a lot during the night; 24 percent say they wake up early and can't get back to sleep at least a few times a week; and 24 percent say "thinking about something" causes them to have difficulty sleeping at least a few nights a week.
In Chinese medicine, insomnia usually means that blood or yin or both are deficient and incapable of nourishing the shen stored in the heart. There is therefore a relative excess of yang and the body is unable to settle down. Excess fire can also disturb the shen.