Dissociation
Etymology
From Latin "dissociare" (to separate), from "dis-" (apart) and "sociare" (to join), itself from "socius" (companion). The psychological sense was developed by the French psychologist Pierre Janet in the late 19th century to describe how parts of the mind can split off from ordinary awareness.
noun · /dih-soh-see-AY-shun/
A mental disconnection from one’s thoughts, feelings, memories, body, or surroundings.
What it names
A precise word for the "checked-out," unreal, or watching-yourself-from-outside experience — from mild spacing out under stress to the protective detachment that follows trauma.
Example
During the accident she felt an eerie dissociation, as if she were calmly watching the whole thing happen to someone else.
Related idea
Milder and more everyday than psychosis (already here), dissociation is a disconnection from reality or self rather than a break producing false beliefs or perceptions.