A patient describes a profound, distressing change in how their own existence feels. Before revealing the answer, decide what distinguishes disturbance of awareness of self-activity from a nihilistic delusion.

Ask whether the patient retains insight that this is simply a strange change in how things feel, or holds a fixed, unshakeable belief. Disturbance of awareness of self-activity differs from a nihilistic delusion in describing a distressing but recognised change in how existence feels, rather than a fixed false belief that one does not exist or is dead. A nihilistic delusion is a fixed belief denying the existence of one's own body, mind, or self, held with full delusional conviction and not amenable to counter-argument, sometimes extending outward to a belief that other people or the world itself have ceased to exist. Whether insight into the change is retained, or a fixed false belief is held instead, is the key distinguishing feature.