Derealisation

Derealisation is the feeling of unreality or detachment with respect to surroundings or external world. The patient may complain of 'everything around me seems like in a dream'. (1)

In majority of patients it is accompanied by depersonalisation. Because the two states typically co-occur and there is no demonstrable evidence to support that they exist independently of one another, a single identification, called depersonalization/derealization disorder (DPDR), has been formally acknowledged by the American Psychiatric Association (APA) and the International Classification of Diseases (ICD) (2)

References:

1. Medford N. Emotion and the unreal self: depersonalization disorder and de-affectualization. Emot Rev. 2012;4(2):139–144.
2. ICD-10 Version. 2019. F48.1 Depersonalization-derealization syndrome (online)