I get it when I am severely depressed and have anxiety. I think it is the anxiety that causes it but not sure. When I am real bad I get borderline psychosis. Anxiety is a new thing for me (oh joy) in the last year I have kind of figured out that the depression comes first, causes the anxiety, then causes paranoia. Depression saps all my self confidence, I fear (based on reality) that I won't be able to function. I can't work, I can't pay my bills, I don't show up for anything, don't honor commitments. The anxiety comes because of all the ways the depression effects my life. Sense of impending doom. The IRS is gonna come at any minute and put me in jail.....on and on.