Ohh sorry I didn't keep looking. Here's a few links.
The History and Psychology
of Spirit Possession and Exorcism
http://www.markbancroft.com/info/spirit-possession#spirit2I have no idea how to copy and paste a Pdf file but here's the link. It's a case study on ten people reporting demonic possession.
http://www.google.co.uk/url?sa=t&rct=j&q=possession%20syndrome&source=web&cd=9&ved=0CGgQFjAI&url=http%3A%2F%2Fulag.net%2Famusing%2Fpossession%2Fexorcism.pdf&ei=PDAeUvmWAonG7AaGi4H4Dw&usg=AFQjCNEDUFfHElCb9OXvBmQdnVEv8pnFEw&bvm=bv.51156542,d.bGEThe Possession Syndrome: A Comparison of Hong Kong and French Findings
http://bjp.rcpsych.org/content/106/442/114.abstractA forensic psychologist on anger, madness and destructive behavior.
by Dr. Stephen Diamond
The idea of demonic possession is nothing less than a metaphysical, theological or spiritual explanation for human evil. The Exorcist (1973), a film based on William Peter Blattey's book about an allegedly true case, provides a highly dramatized depiction of evil, possession and exorcism, and stimulated renewed public fascination with the possession syndrome.
http://www.psychologytoday.com/blog/evil-deeds/201008/giving-the-devil-his-due-exorcism-psychotherapy-and-the-possession-syndromeIs demonic possession real?
http://www.christianitydisproved.com/brain/is-demonic-possession-real.html#reference1This is an abstract from a full article, but it has the option for the full text on the right.
http://isp.sagepub.com/cgi/pdf_extract/17/2/150THE POSSESSION SYNDROME ON TRIAL
http://www.holysmoke.org/cos/postrial.htmThe Devil Inside: Psychotherapy, Exorcism and Demonic Possession
http://www.psychologytoday.com/blog/evil-deeds/201201/the-devil-inside-psychotherapy-exorcism-and-demonic-possessionHow Exorcism Works
http://science.howstuffworks.com/science-vs-myth/afterlife/exorcism5.htmElements of Culture and Mental Health: Critical Questions for Clinicians
http://ajp.psychiatryonline.org/article.aspx?articleid=1722086POSSESSION SYNDROME: AN EPIDEMIOLOGICAL STUDY IN WEST KARNATAKA1
Full text just under the abstract.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3012945/Epileptic seizures and spirit possession in Haitian culture
http://www.ncbi.nlm.nih.gov/pubmed/20724222Mental disease related to belief in being possessed by the "Zar" spirit
http://www.ncbi.nlm.nih.gov/pubmed/7926995The 'Zar' possession syndrome among Ethiopian immigrants to Israel: cultural and clinical aspects
http://www.ncbi.nlm.nih.gov/pubmed/8883974I glanced at them but didn't read them fully, but there seemed to be some interesting stuff.