It may be mistaken for dissociative experiences, dysmorphia, even psychosis. But clients who are plagued by existential doubts and ‘what ifs?’ may actually be experiencing a lesser-known form of Obsessive Compulsive Disorder. Dr Karen Cassiday, clinical psychologist and specialist in anxiety disorders, sets out the key differentiating features of existential OCD – and describes some of the disturbing ideas and desperate behaviours we may notice in its presence.