Elder St. Porphyrios on the Danger of Delusion…
The most dreadful delusion can be created by spiritual prayer. Other prayers are prayed to a large extent by our mind. We simply say them and our ears hear them. They are said in a different way. But spiritual prayer is something else. And if in this spiritual dimension desire is enkindled, not by your good self, but by the other self, the egotistical self, then undoubtedly you will begin to see lights, but not the light of Christ, and undoubtedly you will begin to experience a pseudo-joy. But in your outward life, in your relations with other people, you will be ever more aggressive and irascible, more quick-tempered and fretful. These are the signs of the person who is deluded. The person who is deluded does not accept that he is suffering from delusion. He is fanatical and does harm. This is what happens with zealots, those who act with a zeal that is not tempered by divine knowledge
– ‘Wounded by Love’