Prelest

Image Source: https://anothercity.org/what-is-prelest/

“Prelest (from Russian: прелесть, from Russian: лесть – cajolery (charm, seduction), Greek: πλάνη – plani), also known as: spiritual delusion, spiritual deception, delusion, illusion, – according to Holy Fathers of Orthodox Church, a false spiritual state, a spiritual illness, “a wounding of human nature by falsehood” [as described by St. Ignatius Brianchaninov].
The concept of prelest should not be confused with somatic mental illness of any kind; prelest is rather a spiritual illness, an illness of the soul in its personal relation to God, an illness that originates from vainglory, pride, and demonic suggestion and that is to be cured by humility and Holy Sacraments and under the guidance of the spiritual father.
In the broadest sense, everyone is in prelest: everyone has some wrong thoughts and views, everyone does not fully understand the meaning of life, the degree of own sinfulness etc. When the word “prelest” is used in the narrow sense, i.e. that some particular person is in the state of prelest, that usually means that this person, initially being on the path of pious Christian life, became possessed with the strongest pride and self-conceit right up to the thought about personal sanctity. To consider oneself a saint – that is a clear prelest because the closer a man is to God, the more he sees his imperfection, and all true saints considered themselves in the feeling of the heart the greatest sinners. The state opposite to prelest is spiritual sobriety.”

– https://en.wikipedia.org/wiki/Prelest