Sigmund Freud, in a personal letter, confessed his longstanding fear that he had a real-life double, a doppelgänger: Was Freud delusional?

First, search “Freud” on this site, to see my essay discussing the evidence that Freud had multiple personality (the trait, not the mental illness). This explains his fear that he had a doppelgänger.

Second, search “unconscious,” which Freud neither discovered nor understood.

Freud acknowledged that valid cases of multiple personality had been reported, but his theory of mind could not explain their existence.