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Classification of sleep disorders, as developed in the 19th century, used primarily three categories: Insomnia, Hypersomnia and Nightmare. In the 20th century, increasingly in the last half of it, technological discoveries led to rapid advances in the understanding of sleep and recognition of sleep disorders. Major sleep disorders were defined following the development of Electroencephalography in 1924 by Hans Berger.
Three systems of classification are in use worldwide:
The ICD and DSM lump different disorders together while the ICSD tends to split related disorders into multiple discrete categories. There has, over the last 60 years, occurred a slow confluence of the three systems of classification.
Diagnoses of sleep disorders are based on self-assessment questionnaires, clinical interview, physical examination and laboratory procedures. The validity and reliability of various sleep disorders are yet to be proved and need further research within the ever-changing field of "Sleep Medicine". Admittedly, the development of sleep disorder classification remains as much an art as it is a science.