Word for not feeling part of a social or economic class

Is there a word for a feeling or person that is part of a social class, but doesn't feel like they belong in that class? Say someone was poor their entire life and won the lottery. People they may associate with, and are friends with, poor people but may live around and attend functions with people in their economic class. In those cases they feel out of place.

Not a single word but a common idiom...

be like a fish out of water

To feel awkward because you are not familiar with a situation or because you are very different from the people around you. source

All the other children in the school had rich, middle-class parents, and she was beginning to feel like a fish out of water.

Perhaps alienated

feeling that you do not belong in a particular society, place, or group

Another possibility is anomic

socially disoriented

This, however, usually refers to a breakdown in overall social mores or values.

Parvenu: "a person who has recently or suddenly acquired wealth, importance, position, or the like, but has not yet developed the conventionally appropriate manners, dress, surroundings, etc."

It is derogatory, and the sense of not belonging is legitimate emotion

This may be a case of impostor syndrome:

impostor syndrome … is a psychological phenomenon in which people are unable to internalize their accomplishments. Despite external evidence of their competence, those with the syndrome remain convinced that they are frauds and do not deserve the success they have achieved.

"to feel like an outsider" can fit also and it is a very common phrase.

Though it can be applied pertaining not only to changing environments but also a general feeling of not belonging to any class.

classlessness is a similar concept but less common. It can be used as "to feel classless".

outsider: One who is isolated or detached from the activities or concerns of his or her own community.

classless: characterized by the absence of economic and social distinctions