Christians tell me that is of the devil.

Lies and slander, I’d say. They hypnotized themselves and/or had been hypnotized by other people to think that way.
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No, just delusion.
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No.
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Nope. In hypnosis, you stop acting like an idiot at some point.
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If you take a Catholic service as a standard ritual, there are some simliarities. I’m a hypnosis nut, and the best definitions I’ve found are that hypnosis is an altered state of awareness. You can look at hypnosis and a standard service as gateway rituals. Both take certain steps to changing your perceptions. Most Catholics I know just get really bored during the service, though!

You really get altered states that are more like trance when you go to pentecostal religions– loud music, speaking in tongues, wild emotions.

For just standard Christian prayer, like the Lord’s prayer or prayers asking for stuff, I doubt they take long enough to really be like hypnosis.

However, there is a line of meditation in Christianity that’s a lot like Buddhist meditation. It’s called "apophatic" meditation and was revived in the 70s by a monk name Thomas Keating. It’s all about letting the mind go… which reminds me of hypnosis. I don’t know a lot about it, but I think that the techniques they use for mental self-control are probably a lot like the same ones in self-hypnosis.
References :
http://www.hypnotizeyourselftoday.com/how-to
http://en.wikipedia.org/wiki/Trance
http://www.contemplativeoutreach.org/site/PageServer?pagename=about_people_keating