What is the science behind demonic possession and exorcisms?

I heard on the radio about an exorcism conference being held in the U.S. I was a bit surprised to find demonic possession is still being taken seriously. The article mentions a modern wrinkle of first screening people for physical or mental disabilities. How do we account for those who remain? I wonder if they are just faking it. I think it would be cool to be the center of a drama involving a team of priests invoking all sorts of prayer and ritual and then making everyone so happy by announcing that you have been freed of possession.