There are many carefully documented accounts in the medical literature of intense, life-altering religious experience in epileptic seizures. Hallucinations of overwhelming intensity, sometimes accompanied by a sense of bliss and a strong feeling of the numinous, can occur especially with the so-called "ecstatic" seizures that may occur in temporal lobe epilepsy. Though such seizures may be brief, they can lead to a fundamental reorientation, a metanoia, in one's life. Fyodor Dostoevsky was prone to such seizures and described many of them, including this:
The air was filled with a big noise and I tried to move. I felt the heaven was going down upon the earth and that it engulfed me. I have really touched God. He came into me myself, yes God exists, I cried, and I don't remember anything else. You all, healthy people ... can't imagine the happiness which we epileptics feel during the second before our fit. ... I don't know if this felicity lasts for seconds, hours or months, but believe me, for all the joys that life may bring, I would not exchange this one.
A century later, Kenneth Dewhurst and A. W. Beard published a detailed report in the Journal of Neurology, Neurosurgery, and Psychiatry of a bus conductor who had a sudden feeling of elation while collecting fares. They wrote:
He was suddenly overcome with a feeling of bliss. He felt he was literally in Heaven. He collected the fares correctly, telling his passengers at the same time how pleased he was to be in Heaven. ... He remained in this state of exaltation, hearing divine and angelic voices, for two days. Afterwards he was able to recall these experiences and he continued to believe in their validity. [Three years later] following three seizures on three successive days, he became elated again. He stated that his mind had "cleared." ... During this episode he lost his faith.
He now no longer believed in heaven and hell, in an afterlife, or in the divinity of Christ. This second conversion -- to atheism -- carried the same excitement and revelatory quality as the original religious conversion.
More recently, Orrin Devinsky and his colleagues have been able to make video EEG recordings in patients who are having such seizures, and have observed an exact synchronization of the epiphany with a spike in epileptic activity in the temporal lobes (more commonly the right temporal lobe).