paranoia

noun. mental illness characterized by systematized delusions of persecution or grandeur usually without hallucinations

• Psychotic symptoms and paranoia persisted, and she continued to "find clues" of conspiracy against her.
• … Arthur Miller dramatized the ways that a society's paranoia and fear during periods of uncertainty and change can turn into a witch hunt.

noun. a tendency on the part of an individual or group toward excessive or irrational suspiciousness and distrustfulness of others