Disruptions in the natural cycles of sleep and waking are considered to be sleep disorders. It is estimated that 15 percent of people have some form of sleep disorder or another.
As we grow older the insomnias become more prevalent, but these disorders can occur at any age. Some of the conditioning that society requires can create stress or conflict between the demands on an individual to sleep on schedule and the individuals natural cycle and patterns of wakefulness and sleepiness. Jet lag is an example of sleep disorder that comes from travelling over many time zones, and can be quite incapacitating. Night shift workers who change back and forth to mid or day shifts can experience societally imposed external demands that conflict with natural rhythms in sleeping and waking.
There are five categories of sleep disruption: Primary, which is unrelated to any internal physical or mental problem, and secondary, which is related to physical or psychological disorder or drugs and alcohol. With the secondary causes, there are medical and psychiatric disorders that are related to insomnias and there are medications and substances that relate to insomnias. There are also parasomnias and dyssomnias. Finally there is sleep disorder related to another mental disorder.
In primary insomnia, there is either difficulty in getting to sleep, or there is waking up from sleep. The problem can be severe enough to interfere with functioning well enough to meet the demands of society, which include waking up refreshed enough to get to work and to perform well, not falling asleep during the daytime, sleeping through the night, and being sharp and wakeful at other times, such as socializing.
Dyssomnias occur when the quality, timing or amount of sleep is disrupted. Parasomnias relate to abnormal behavorial or psychological events that occur while sleeping.
Of the dyssomnias, there are three types of primary insomnias: sleep onset, sleep maintenance, and terminal. Sleep onset implies difficulty getting to sleep. Sleep maintenance implies difficulty staying asleep. And Terminal implies early waking with inability to get back to sleep.
Primary hypersomnia is a dyssomnia that involves excessive sleepiness at any time, day or night. Narcolepsy, breathing related sleep disorder and circadian rhythm sleep disorder are also dyssomnias.
Of the parasomnias, there is nightmare disorder, sleep terror disorder, and sleepwalking disorder. Teeth grinding (bruxism) and bed wetting (enuresis) are also features of the parasomnia class of sleep disorders.
Common with males, the night terror, sleepwalking and nightmare disorders can result in violent or dangerous incidents that require treatment due to the possibility of harm to others or to the self. Drug treatment by clonazepam and carbamazepine are common in these cases.
The final category is sleep disorders that are related to other mental disorders. These most often apply to, but are not limited to mood or anxiety disorders that are able to be diagnosed.
Encyclopedia of Mental Disorders: Sleep Disorders