It may not be relevant, but if you did not find any, you can make your own ontology with OntoGen ( http://ontogen.ijs.si/ ). I already did it for the sport corpus.
I have worked with the Protege tool (http://protege.stanford.edu/). There you'll find tutorials that will guide to creation/modification of ontologies.
I think you might want to check out the UMLS - this is a warehouse of many different medical ontologies, and includes a lot of content relating to mental illness and other sorts of conditions that relate to psychology. For example I did a quick check and there are more than 700 concepts in the UMLS relating to the term "depression".
http://www.nlm.nih.gov/research/umls/
Note that while the UMLS is coordinated by the NLM in the USA, it is available outside the USA as well, and there is no cost (although a license agreement is required).
Are you interested in ALL of psychology or a subdomain? The Mental Functioning Ontology, the Emotion Ontology, and the Personality Assessment Ontology are all available on Github. See also, Blanch, Angel et al. "Ontologies About Human Behavior" European Psychologist (2017), 22(3), pp. 180-197.