Elder Ephraim of Philotheou. "My life with elder Joseph".
(translated from Russian)
The Elder [Joseph the Hesychast] told us: "Have you seen the monk, who fell into sin, who became a deserter? It happened to him because he concealed his thoughts. He did not disclose them - and they killed him, like the snakes kill. Newly hatched little snakes are small, but if you do not drive them away, they will grow and become poisonous. One of them will bite you, and you will die. Have you seen a man in delusion? It happened to him because of the thoughts."
The Elder told us about some people who concealed their thoughts and suffered from that, fell into delusion. Such people quite often committed suicide because they believed that an Angel appeared to them, whereas it was a demon. The delusion was in the thought: "Do not tell that to the Elder".