A patient describes several days of a vague but powerful sense that something important is happening around him and that it concerns him personally, though he cannot say what it actually is, accompanied by marked unease, before this feeling resolves into a specific, crystallised belief. What is this?

This is delusional mood: a pervasive sense that something important or personally significant is happening, without any clear idea of what, often accompanied by marked anxiety or unease, and frequently resolving once a specific delusional perception or sudden idea gives the vague feeling concrete meaning, exactly as described. It is not a delusional perception, since that involves a specific, crystallised delusional meaning attached to a normally perceived stimulus, which delusional mood by definition lacks — it is the unformed state that often precedes it. It is not generalised anxiety, which lacks the specific quality of personal significance about unfolding events that characterises delusional mood. And it is not perplexity, which is a bewildered inability to make sense of experience, rather than this particular sense of unfolding personal significance.