This section is from the "Nature Cure: Philosophy and Practice Based on the Unity of Disease and Cure" book, by Henry Lindlahr.
While the alternate breathing exercises are very valuable for overcoming obstructions in the air passages, for establishing the habit of rhythmic breathing and for refining and accelerating the vibratory activities on the physical and spiritual planes of being, they must be practiced with great caution. These, and other "Yogi" breathing exercises, are powerful means for developing abnormal psychical conditions. They are therefore especially dangerous to those who are already inclined to be physically and mentally negative and sensitive. Such persons must avoid all practices which tend to refine excessively the physical body and to develop prematurely and abnormally the sensory organs of the spiritual body. The most dangerous of these methods are long extended fasting, raw food diet, that, is, a diet consisting of fruits, nuts, oils and raw vegetables and excluding the dalry products, "Yogi" breathing, and "sitting in the silence." That is, sitting in darkness, in seclusion or in company with others, while keeping the mind in a passive, receptive condition for extraneous impressions. These practices tend to develop very dangerous phases of abnormal and subjective psychism, such as clairvoyance, clairaudience, mediumship and obsession.