Kennedy (1976) described 2 cases in which de-personalisation appeared to be triggered by meditation. The first case developed after the subject used breathing and meditation exercises described in a book on self-development. The experience continued for at least 16 months. The second case involved the use of meditation techniques recommended by the Arica Institute. While at first pleased with the experiences, the subject soon found he was unable to maintain a job and needed professional help.
More information about Kennedy’s study and the adverse effects of meditation can be found at Dr Ramesh Manocha’s blog.