The Dissociative Experiences Scale (DES) is a simple, quick, self-administered questionnaire that has been widely used to measure dissociative symptoms. It has been used in hundreds of dissociative studies, and can detect depersonalization and derealization experiences. The Dissociative Disorders Interview Schedule (DDIS) is a highly structured interview which makes DSM-IV diagnoses of somatization disorder, borderline personality disorder and major depressive disorder, as well as all the dissociative disorders. It inquires about positive symptoms of schizophrenia, secondary features of dissociative identity disorder, extrasensory experiences, substance abuse and other items relevant to the dissociative disorders. The DDIS can usually be administered in 30–45 minutes. The Cambridge Depersonalization Scale (CDS) is a method for determining the severity of depersonalization disorder. It has been proven and accepted as a valid tool for the diagnosis of depersonalization disorder in a clinical setting. It is also used in a clinical setting to differentiate minor episodes of depersonalization from actual symptoms of the disorder. Due to the success of the CDS, a group of Japanese researchers underwent the effort to translate the CDS into the J-CDS or the Japanese Cambridge Depersonalization Scale. Through clinical trials, the Japanese research team successfully tested their scale and determined its accuracy. One limitation is that the scale does not allow for the differentiation between past and present episodes of depersonalization. It may be difficult for the individual to describe the duration of a depersonalization episode, and thus the scale may lack accuracy.
While brief episodes of depersonalization or derealization can be common in the general population, the disorder is only diagnosed when these symptoms cause substantial distress or impair social, occupational, or other important areas of functioning. Signs and symptoms
The core symptoms of depersonalization-derealization disorder is the subjective experience of "unreality in ones self", or detachment from ones surroundings. People who are diagnosed with depersonalization also often experience an urge to question and think critically about the nature of reality and existence.Individuals with depersonalization describe feeling disconnected from their physicality; feeling as if they are not completely occupying their own body; feeling as if their speech or physical movements are out of their control; feeling detached from their own thoughts or emotions; and experiencing themselves and their lives from a distance. While depersonalization involves detachment from ones self, individuals with derealization feel detached from their surroundings, as if the world around them is foggy, dreamlike, or visually distorted. Individuals with the disorder commonly describe a feeling as though time is passing them by and they are not in the notion of the present. In some cases, individuals may be unable to accept their reflection as their own, or they may have out-of-body experiences. One-third to one-half of patients with DPDR also experience hearing internal voices. This is to differentiate from external voices which are more commonly found in psychosis. Additionally some individuals experience difficulty concentrating and problems with memory retrieval.