In A Hermit in the Himalayas, I have told of those practisers of hatha yoga who held their breath too long and exploded a blood vessel in the lungs, causing serious injury. There are others, however, who have been luckier, for with them the exploded vessel is in the brain, but it has not gone far enough to cause a paralytic stroke. It has gone far enough, though, to disrupt those parts of the brain which concern past memory and future anticipation, so that the yogi is left with a consciousness dwelling only in the immediate moment. This is something like The Eternal Now sensed by the philosopher and gives the yogi a kind of peace, a freedom from cares and fears. He will then declare that he has entered samadhi, not understanding that he has become a case for medical attention. His physical movements will slow down to the point of uncertainty, his fellow yogis will admire his attainment and become his followers, and he will become a guru!
-- Notebooks Category 5: The Body > Chapter 5: Exercise > # 103