[Although he's giving her pretty much the exact same lecture he gave Itachi, the tone is much, much softer. The hand squeeze may have helped.]
Paranoia is a mental illness heavily influenced by anxiety and fear, often to the point of irrationality and delusion. Its main characteristics typically include percecutory beliefs, perceived threats towards oneself - often of a conspiratory nature - general distrust and a compulsion to make false accusations.
It's typically diagnosed in individuals suffering from paranoid schizophrenia, the persecutory type of delusional disorder called querulous paranoia or as a paranoid personality disorder.
It's an illness, not something you choose in order to be more vigilant.