In this fascinating video, Christian apologist Sean McDowell (Josh's son), interviews Dr. Richard Gallagher, a board-certified psychiatrist and a professor of psychiatry at New York Medical, and a psychoanalyst on the faculty of Columbia University. Dr. Gallagher graduated from Princeton University and trained as a resident in psychiatry at Yale University School of Medicine. In this video, he discusses making a determination of a patient's possession - first by ruling out underlying illnesses, psychiatric conditions, psychosis, etc. He's been described as being world’s foremost scientific expert on the subject of diabolic attacks. He says that Hollywood films have sensationalized and distorted the process (at least as practiced by Western, professional psychiatric professionals in conjunction with Protestant and Catholic clergy, which he describes as being considerably different, noting that clergy are often who he is contacted by to evaluate a case history and patient. He also describes circumstances and activities that appear to have opened the patient up to possession or oppression (he differentiates between the two).
https://www.youtube.com/watch?v=ZfunNURoO2w
Also, here is a good overview of the passages of demon possession and deliverance recorded in the New Testament: https://digitalcommons.andrews.edu/cgi/ ... ntext=jams