Derealization (sometimes abbreviated as DR) is an alteration in the perception or experience of the external world so that it seems unreal. Other symptoms include feeling as though one's environment is lacking in spontaneity, emotional coloring, and depth. It is a dissociative symptom of many conditions including severe stress, trauma, depression and anxiety.
Derealization is a subjective experience of unreality of the outside world, while depersonalization is sense of unreality in one's personal self, although most authors currently do not regard derealization (surroundings) and depersonalization (self) as separate constructs.
Chronic derealization may be caused by occipital–temporal dysfunction. These symptoms are common in the population, with a lifetime prevalence of up to 5% and 31–66% at the time of a traumatic event.
The detachment of derealization can be described as an immaterial substance that separates a person from the outside world, such as a sensory fog, pane of glass, or veil. Individuals may report that what they see lacks vividness and emotional coloring. Emotional response to visual recognition of loved ones may be significantly reduced. Feelings of déjà vu or jamais vu are common. Familiar places may look alien, bizarre, and surreal. One may not even be sure whether what one perceives is in fact reality or not. The world as perceived by the individual may feel as if it were going through a dolly zoom effect. Such perceptual abnormalities may also extend to the senses of hearing, taste, and smell. The degree of familiarity one has with their surroundings is among one's sensory and psychological identity, memory foundation and history when experiencing a place. When persons are in a state of derealization, they block this identifying foundation from recall. This "blocking effect" creates a discrepancy of correlation between one's perception of one's surroundings during a derealization episode, and what that same individual would perceive in the absence of a derealization episode.
Frequently, derealization occurs in the context of constant worrying or "intrusive thoughts" that one finds hard to switch off. In such cases it can build unnoticed along with the underlying anxiety attached to these disturbing thoughts, and be recognized only in the aftermath of a realization of crisis, often a panic attack, subsequently seeming difficult or impossible to ignore. This type of anxiety can be crippling to the affected and may lead to avoidant behavior. Those who experience this phenomenon may feel concern over the cause of their derealization. It is often difficult to accept that such a disturbing symptom is simply a result of anxiety, and the individual may often think that the cause must be something more serious. This can, in turn, cause more anxiety and worsen the derealization. Derealization also has been shown to interfere with the learning process, with cognitive impairments demonstrated in immediate recall and visuospatial deficits. This can be best understood as the individual feel as if they see the events as if in third person, therefore he or she cannot properly process information especially through the visual pathway.
People experiencing derealization describe feeling as if they are viewing the world through a TV screen. This, co-morbidities such as depression and anxiety, and other similar feelings attendant to derealization, can cause a sensation of alienation and isolation between the person suffering from derealization and others around them. This is particularly the case as Derealization Disorder is characteristically diagnosed and recognized sparsely in clinical settings. This is in light of general population prevalence being as high as 5%, skyrocketing to as high as 37% for traumatized individuals.
Partially symptoms would also include a feeling of being an "observer"/having an "observational effect". As if existing as a separate entity on the planet, with everything happening, being experienced and alternately perceived through their own eyes (similar to a first person camera in a game, e.g. Television or Computer-Vision).
Derealization can accompany the neurological conditions of epilepsy (particularly temporal lobe epilepsy), migraine, and mild TBI (head injury) There is a similarity between visual hypo-emotionality, a reduced emotional response to viewed objects, and derealization. This suggests a disruption of the process by which perception becomes emotionally coloured. This qualitative change in the experiencing of perception may lead to reports of anything viewed being unreal or detached.
Some neurophysiological studies have noted disturbances arising from the frontal-temporal cortex, which as noted was highly correlated in temporal-lobe disorders such as epilepsy. This lead to speculation of involvement of more subtle shifts in neural circuitry and inhibitory neuro-chemical pathways.
Derealization can possibly manifest as an indirect result of certain vestibular disorders such as labyrinthitis. This is thought to result from anxiety stemming from being dizzy. An alternative explanation holds that a possible effect of vestibular dysfunction includes responses in the form of the modulation of noradrenergic and serotonergic activity due to a misattribution of vestibular symptoms to the presence of imminent physical danger resulting in the experience of anxiety or panic, which subsequently generate feelings of derealization. Likewise, derealization is a common psychosomatic symptom seen in various anxiety disorders, especially hypochondria. However, derealization is presently regarded as a separate psychological issue due to its presence with several pathologies or idiopathically.
Derealization and dissociative symptoms have been linked by some studies to various physiological and psychological differences in individuals and their environments. It was remarked that labile sleep-wake cycles (labile meaning more easily roused) with some distinct changes in sleep, such as dream-like states, hypnogogic, hypnopompic hallucinations, night-terrors and other disorders related to sleep code possibly be causative or improve symptoms to a degree  Derealization can also be a symptom of severe sleep disorders and mental disorders like depersonalization disorder, borderline personality disorder, bipolar disorder, schizophrenia, dissociative identity disorder, and other mental conditions.
Cannabis, psychedelics, dissociatives, antidepressants, caffeine, nitrous oxide, albuterol, and nicotine can all produce feelings mimicking feelings of derealization, particularly when taken in excess. It can also result from alcohol withdrawal or benzodiazepine withdrawal. Opiate withdrawal can also cause feelings of derealization, whose symptoms can be protracted (chronic), delayed-onset or possibly instigated by such events, exhibiting high variability in inter-personal subjectivity of the phenomenon.
Derealization can also be a symptom of severe sleep disorders and mental disorders like depersonalization disorder, borderline personality disorder, bipolar disorder, schizophrenia, dissociative identity disorder, and other mental disorders of a similar manner.