true identity; true form; true colors
Refers to the real nature or identity of someone or something, often when it is hidden or disguised. Common in phrases like 正体を現す (reveal one's true self) or 正体不明 (unidentified).
The man's true identity is still unknown.
He finally showed his true colors.
consciousness; one's senses
Used in set expressions like 正体を失う (lose consciousness) or 正体がない (be unconscious/senseless). This usage is somewhat literary or formal.
He drank so much he lost consciousness.
I was so exhausted I nearly passed out.
The suspicious man finally revealed his true identity in the end.
He got so drunk that he lost consciousness.
He had been living all along while hiding his true identity.
The scientists tried to figure out the true nature of the glowing phenomenon.