304 Dissociative Disorders
the symptoms. Less than 20% of individuals experience onset after age 20 years and only
5% after age 25 years. Onset in the fourth decade of life or later is highly unusual. Onset can
range from extremely sudden to gradual. Du ration of depersonalization/derealization
disorder episodes can vary greatly, from brief (hours or days) to prolonged (weeks,
months, or years). Given the rari ty of disorder onset after age 40 years, in such cases the in-
dividual should be examined more closely fo r underlying medical conditions (e.g., brain
lesions, seizure disorders, sl eep apnea). The course of the disorder is often persistent.
About one-third of cases involve discrete episodes; another third, continuous symptoms
from the start; and still another third, an initially episodic co urse that even tually becomes
continuous. 
While in some individuals the intensity of symptoms can wax and wane considerably,
others report an unwavering level of intensity that in extreme cases can be constantly pres-
ent for years or decades. Internal and extern al factors that affect  symptom intensity vary
between individuals, yet some typical pattern s are reported. Exacerbations can be trig-
gered by stress, worsening mood or anxiety symptoms, novel or over stimulating settings,
and physical factors such as lighting or lack of sleep. 
Risk and Prognostic Factors 
Temperamental. Individuals with depersonalization/ derealization disorder are charac-
terized by harm-avoidant temperament, imma ture defenses, and both disconnection and
overconnection schemata. Imma ture defenses such as idea lization/devaluation, projec-
tion and acting out result in deni al of reality and poor adaptation. Cognitive disconnection