Here is wikipedia of "derealization" --
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 complain 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. The world as perceived by the individual may feel like it is 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 a person is 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 affects the learning process. Because the individual almost sees the events as if in 3rd person, they cannot properly process information.
People suffering from derealization have described feeling as if the world external to them were something in a TV show or movie, or as if they were viewing it through a TV screen. This, and other similar feelings attendant to derealization, can cause a sensation of alienation and distance between the person suffering from derealization and others around them.