A patient looks at a real chair across the room and reports that it appears tiny, as though seen from a great distance, though she knows perfectly well it is an ordinary-sized chair nearby. What is this?

This is dysmegalopsia, specifically the micropsia pattern: a real object is correctly identified but its apparent size is distorted, with the person retaining awareness that this does not match how the object actually measures, exactly as described. It is not a visual hallucination, since dysmegalopsia differs from the Lilliputian hallucination described under visual hallucination, in which tiny figures are seen where nothing real is present, rather than a real object being misjudged in size. It is not derealisation, which is a pervasive altered sense that the environment feels unreal or unfamiliar, rather than a specific, measurable distortion of one real object's size. And it is not a body image disturbance, which concerns the felt image of one's own body rather than the perceived size of an external object.