Obsessive thoughts, erratic mood swings, insomnia, loss of appetite, recurrent and persistent images and impulses, superstitious or ritualistic compulsions, delusion, the inability to concentrate -- exhibiting just five or six of these symptoms is enough to merit a diagnosis of a major depressive episode. Yet we all subconsciously welcome these symptoms when we allow ourselves to fall in love. In Love Sick, Dr. Frank Tallis, a leading authority on...