From a psychiatrist's perspective, religion can be considered a delusion or illness (The God Delusion). This is why many religions are anti-psychiatry (Scientology is very anti-psychiatry). Hearing voices (God, angels, or demons) is a symptom of psychosis in mental illness. Speaking in tongues? Exorcisms? Religious delusions are common among the mentally ill and as we know the "sane" too. There is a book called the Three Christs of Ypsilanti about three schizophrenic patients that thought they were Jesus. Prayer is trying to talk to "God." Anyone that talks to God needs an antipsychotic and a mood stabilizer. I should know, part of my bipolar when I am manic is religiosity and obsession over existence of God, religion, the meaning of life and death. When I am stable, I am more rational and atheist in my thinking.
http://www.bible.ca/psychiatry/psychiatr...hrenic.htm
http://www.bible.ca/psychiatry/psychiatr...hrenic.htm