Any insights on when does introversion end and psychosis begins?

Psychosis is...: ... a loss of "reality-testing", i.e., not knowing what is real. The most common examples are hallucinations, where something (a voice, a vision) looks or sounds real but isn't, and delusions, where a belief about the world seems completely and convincingly real, but isn't. "Internal preoccupation," which may look like introversion, also occurs, but isn't enough to define psychosis by itself.