Although the clinical symptoms of severe depression are easily recognized, this is not always the case in minimal forms or in certain masked depressions. Failure to respond to appropriate treatment may then be taken to indicate the possible existence of specific and organic sleep disorders with clinical symptoms similar to those of depressive illness. Sleep disorders mainly comprise sleep apnea and periodic movement of the lower limbs. Diagnosis can only be confirmed by EPS before a specific treatment is selected : correct diagnosis of the disorder is essential, particularly for sleep apnea, since standard drug therapy for depression and anxiety disorders often includes benzodiazepines, which, through the depressant effect they exert on the respiratory centers, only worsen symptoms.