Personality disorders are classes of mental illnesses characterized by inflexible and unhealthy patterns of thinking, feeling, and behaving. Symptoms vary depending on the type of personality disorder. For example, a person with borderline personality tends to have disturbed ways of thinking, impulsive behaviour and problems controlling their emotions. They may have intense but unstable relationships and worry about people abandoning them. But a person with paranoid personality disorder finds it hard to trust others. They might think that people are lying to or manipulating them, even when there is no evidence of this happening.