Dr Manocha describes the historical accounts of adverse effects arising from the use and misuse of meditation in this excerpt from his thesis:
“Popular myth and legend describe how the use of meditation in attempts to invoke supernatural powers and extraordinary capabilities has typically lead to Faustian consequences. Some meditation traditions describe common patterns of adverse effect. For example, the Zen tradition describes unpleasant experiences associated with meditation, that can be terrifying and are not unlike visual hallucinations with delusional content. Similarly, St. John of the Cross described the false enchantments that may tempt the aspirant in prayer, warning that “devils may come in the guise of angels”. That is, that harmful events during meditation can occasionally take the form of what the novice might mistake for spiritual progress.”