I recently had the opportunity to pose this question to an audience of neuroscientists, cognitive psychologists, roboticists, and philosophers at a workshop run by the Swiss Center for the Affective Sciences. Opinion varied widely. Some people had affirmative intuitions; others were in the negative.
Like paradigmatic emotions, feelings of familiarity and unfamiliarity have an affective component. They seem to also be valenced. But there are differences. A feeling of unfamiliarity does not seem to generate physiological action tendencies in the same way that the standard emotions do. And the feeling does not seem to be evaluative in a way that emotions are thought to be. (For instance, to fear a dog is to represent the dog as dangerous; to be sad about a death is to represent it as a loss. Being dangerous and being a loss are evaluative properties. The feeling of unfamiliarity represents its object as unfamiliar, but unfamiliarity is not an evaluative property.)
here and here.) Admiration and contempt are other emotions that don't obviously prompt behavioral action tendencies. Secondly, perhaps being non-evaluative is not enough to keep a mental state from being an emotion.
Debates about whether an X is a Y can often turn out to be mere terminological debates. The question "Is a feeling of unfamiliarity an emotion?" might be answered by asking "what do you mean by 'emotion'?" But the project needn't be merely stipulative; asking this second question might itself be theoretically fruitful. If we consider delusional feelings to be genuine emotions, we might discover important similarities between feelings of unfamiliarity, the feelings that give rise to other delusions, and other paradigmatic emotions.
We might discover, as I suspect, that the division between delusions and disorders of emotion is not as deep as diagnostic manuals would have us believe. Delusions should be thought of as emotional disorders, and emotional disorders such as phobias or pathological anxiety will reveal themselves to involve temporary delusion-like convictions.