Encyclopaedic Dictionary of Buddhism. Samir Nath. Vol. 1. Sarup & Sons. New Delhi. 1998.
"Yoga does have pitfalls and dangers, as does any occult study. The serious student ideally should work under the supervision of a guru or other teacher. The dangers of yoga are extreme introversion, spiritual hedonism, regression (especially with unprepared novices), and emotional fixation on the guru."