The many facets of poor sleep.

Insomnia is a syndrome composed of symptoms of disturbed sleep, decrement of day-time performance and depressed mood to various degrees and in various combinations. This article roughly describes the methods of measuring the different facets of insomnia. A major difficulty in research with insomniacs is seen in the fact that many methods have been developed in research with young healthy volunteers, not with insomniacs. While good sleep is a homogeneous phenomenon, and its quality will be described similarly well by different methods, insomnia is a very heterogeneous syndrome with low intercorrelation of the different measures. Therefore, insomniacs' sleep quality should be assessed from as many points of view as possible.