"Never accept any physical or spiritual appearances, either outside or inside yourself, even if it might be an image of Christ, or an angel, or some Saint, or if light should appear, or imprint itself in the mind...
Be attentive, that you may not come to believe something, even if it is something good, and be not captivated by it before consulting those who are experienced and are able to analyze the matter, so that you do not suffer harm...
God is not displeased with the person who is attentive to himself, even if he, out of fear of deception, does not accept even that which is from Him, without consulting and testing..."
~St Gregory the Sinaite
I used to do a lot of psychedelics, and am unfortunately susceptible to imaginations. The above quote has helped me tremendously