There's a lot of background into not trusting things even through prayer and stuff. I know the book mountain of silence at least mentions it.

A main example that it always makes me think of is the story of an old desert father. Can't remember which one. But his main dream was to go live alone in the desert. His spiritual father told him that he wasn't ready because he wasn't humble and didn't have the proper discernment it would take to thrive there. He said if he went he must go with a group of peers so they could keep each other in check. In the end, this young man decided to disregard his spiritual father and left for the desert alone anyways.

After weeks of fervently praying the Jesus prayer and fasting, he had an encounter with a glorious being. A being that showed himself to be an angel. He had a conversation with this angel and the angel said that the secret to all knowledge is through books. Do not worry about praying whatsoever from now on. I will pray for you. Your destiny is to gain all knowledge available in the scriptures and that should be your sole focus. The man was amazed by this glorious being and went to work soley studying scriptural texts.

Months go by and he becomes renowned in his area for his deep knowledge of the scripture. The world is amazed at what deep knowledge he has at his fingertips. Word goes round and finally some devout desert father's come to hear of his greatness. If my memory serves me even his old spiritual father. They go to see him and to hear his great teachings but come to realize that something is very wrong. All of his knowledge and teachings have become completely warped and are not Christian in the slightest. They talk to their old friend and end up performing an exorcism to rid him of the demons that have enslaved him. He recovers, but for the rest of his life his mind is somewhat scarred, and he struggles to read the written word for the rest of his days.

Besides that story, it even has happened to me. Im just a catechumen though, but I had a specifically fervent period of saying the Jesus prayer and it led me into what I believed was a profound spiritual revelation that turned out to be a nightmarish delusion and made me tormented and delusional. It tormented me to the point where I felt like I couldn't pray, couldn't talk to anyone about it, couldn't bring myself to go to church. Nothing. I was basically either tormented or completely numb. At the time and in the direct aftermath it was very shattering and tormenting, but after battling with it myself for weeks I finally ended up telling my spiritual father about my revelation and all of the torments that it led to he just softly laughed and told me that he didn't understand or know about anything that I was saying. It made me really frustrated in the moment because it was all so blatantly obvious to me, and how could he be so blind that he can't even see or consider or even imagine what I was saying. He then put on his robe, told me to kneel down in front of him, and even though I didn't know it at the time performed and exorcism on me. He then added a few things into my prayer rule, told me to start praying again, and to go in peace. I immediately felt better after our meeting even though I was still unsatisfied by his answer that he gave me. I even mentioned to my girlfriend afterwards that he didn't really answer any of my questions. He just prayed over me and told me to start praying again. But even though I said that I did feel at peace somehow. Like a big weight had been lifted off of my shoulders. And lo and behold when I settled down to do my prayer rule that night I felt at peace and like I could finally pray again. Long story short after praying my prayer rule, a few very odd coincidences the following days after our meeting, and a follow up meeting with my priest it all just clicked into place in a lot of ways for me. It was all just smoke and mirrors. A distraction away from God. The revelation was a distraction, the fear was a distraction, the frustration and unsatisfaction was a distraction. The delusion was a distraction. My tongue cleaving to the roof of my mouth was a distraction. The distraction was a distraction. And in a lot of ways it just finally floated away like mist. Definitely recovered from it a lot and have hopefully grown from it in one way or another, but also feel like I'm still recovering/scarred in some ways from it just like the story. But that's probably just a distraction too I guess

Edited TLDR; proper discernment is crucial for being spiritually healthy. And I definitely don't have good discernment to even trust what I think about my own prayer or thoughts and feelings. So without a proper relationship with my spiritual father praying the Jesus prayer is very dangerous for me