Alix, I think the problem Christians have with yoga and meditation is they do not understand the philosophy, and this is partly because they do not understand these main concepts used in Yoga: consciousness(chitta), self(atman), ego(ahamkara )and mind(manas).
In Western philosophy consciousness, self, ego and mind are all taken to be the same thing and this is why there is so much confusion. In Yoga they are not the same thing and very precise definitions are given:
Consciousness: This is the spirit
Self: This is the observer or seer
Ego: This is the personality(I-am-that-ness)
Mind: This is the network of thoughts
So when Yoga tells you to cease the thoughts or empty the thoughts it is only asking you to cease the mind and the ego. It is not telling you to cease or empty the self.
Now it will be demonstrated to you using an extreme example what the mind and ego can do. Suppose you are a teacher at a school and the children are not listening to you and are mocking you. You then experience thoughts and feelings of anger, frustration and think to yourself, “I am the teacher here, they should listen to me” Before you know it you are shouting at the children. They mock you even more. You get more angry, and quick flashes of memories flash by in the screen of your mind of other times when you were mocked. Before you know it you are hurling abuses at the children yourself.
Why did all of this happen? It happened because rather than you controlling your mind, your mind was controlling you. You were a slave to the network of thoughts it brought up and a slave to the limited sense of self “I am the teacher” The mind completey overwhelmed you with its thoughts.
But what if you had from the very start not identified with the thoughts, “I am the teacher, they shoud listen to me” then you woud have stopped the mind right in its tracks and prevented it from creating more drama of thoughts. This would have given you the power to respond with a clearer perception.
What can we learn from this? We learn that we are separate from our thoughts. They have no power over us unless we give them power. We also learn that thoughts when they take place disturb our perception. Finally, if we are indeed separate from our thoughts then we can exist without thoughts altogether and still be aware of self(this is called thoughtless awareness). If our perception becomes clearer by losing some thoughts, then it become absolutely clear when we lose all the thoughts.
This is something Christians need to realise, it is not thoughts which gives them power, but pure awareness. In the light of pure awareness nothing false can stand. So if Christians are really afraid of demons getting hold of them, they are far more vulnerable to demons when they are less-aware than more aware. When they are absolutely aware then they are then in the same divine space as god(holy spirit).
A Yogi does not have to worry about demons, deception or fallacy, because their perception is so acute, they can catch anything, no matter how minute or subte. So can Christians if they practice Yoga and meditation. Demons would not dare come before a realised yogi. The yogi would spot them from a mile.