Someone who sees things that no one else can see is having a psychotic episode. They need help right away. Usually anti-psychotic medicine will help. Certain illegal drugs cause hallucinations. Someone is paranoid if they think someone is trying to kill them, or poison them.
Loners like to stay to themselves and are more prone to depression.
Anxiety disorders and phobias. Some people have a hard time controlling their impulses. Those who have disruptive mood swings have bipolar disorder, also called manic-depression. They have mood swings from mania to depression. Those who have a criminal record usually have antisocial behavior.