The Yogi says there is a great danger in stumbling upon this state. In a good many cases there is the danger of the brain being deranged, and, as a rule, you will find that all those men, however great they were, who had stumbled upon this super conscious state without understanding it, groped in the dark, and generally had, along with their knowledge, some quaint superstition. They opened themselves to hallucinations. Mohammed claimed that the Angel Gabriel came to him in a cave one day and took him on the heavenly horse, Harak, and he visited the heavens. But with all that, Mohammed spoke some wonderful truths. If you read the Koran, you find the most wonderful truths mixed with superstitions. How will you explain it? That man was inspired, no doubt, but that inspiration was, as it were, stumbled upon. He was not a trained Yogi, and did not know the reason of what he was doing. Think of the good Mohammed did to the world, and think of the great evil that has been done through his fanaticism! Think of the millions massacred through his teachings, mothers bereft of their children, children made orphans, whole countries destroyed, millions upon millions of people killed!
So we see this danger by studying the lives of great teachers like Mohammed and others. Yet we find, at the same time, that they were all inspired. Whenever a prophet got into the superconscious state by heightening his emotional nature, he brought away from it not only some truths, but some fanaticism also, some superstition which injured the world as much as the greatness of the teaching helped.
Swami Vivekananda Complete works : Volume 1 : Raja Yoga