Letters of St. Ambrose of Optina. Letter 390.
You write about your brother who suffers from mental illness of suspicion, as if the secret police is chasing him everywhere and through everyone, so he suspects evil intents and connections with the secret police in the people closest to him. This mental disease had occurred to him due to the fact that he was ashamed, or simply did not want to repent of his childhood sins considering them unimportant. But conscience – the incorruptible judge – reminded him with its reproaches of the need to repent, suggesting that he is wrong and is to blame; but he, instead of repenting, turned the reproaches of the conscience into a police pursuit. When this was joined by unbelief and long refusal of the communion of the Holy Mysteries, it further strengthened his mental illness of unfounded suspicion.
You are afraid that he will become completely mad... But it is the lightest evil and misery. In this case, at least, his life would be saved, if he is in the insane institution, and a man in madness is no longer responsible for what he does in this condition. Of course, he shall bear responsibility for the previous deeds.
It will be good, if you could manage to bring your brother to the monastery of St. Sergius and to serve with him a prayer service in the caves before the miraculous icon of Our Lady of Chernigov, having arranged beforehand a good confessor for your brother. After the prayer before this icon, the mentally damaged people came to the common sense and confessed well and were healed through it.