I am no expert on this topic but I could find a legitimate sourc, the book : Yoga: frredom and Immortality" by Mircea Eliade, a well known religious scholar.
Excerpts from the book:
The gradual spread of Yoga practice can be traced both in juridico-theological literature and in the didactic and religious portions of the Mahabharata. Yet, it would be diificult to define the successive stages of inflirtation, which will finally result in the almost total conquest of Indian spirituality by yoga…
The planting of Yoga techniques in the very heart of Hinduism took place at a moment of crisis for orthodoxy (Brahmanism)…
What it is called “Hinduism” dates from the still little known period when the ancient Vedic pantheon was eclipsed by the enormous popularity of a Siva, a Visnu, or a Khrishna…
You will find lots of lots of info in this classic book. Actually you can download the book
from the site
http://www.4shared.com/account/document/vUeoIKce/2__Mircea_Eliade-_YOGA_IMMOR.html
A thorough study is necessary before rushing in with answers.
A few things about the author, Mircea Eliade:
He was a renowned scholar and university professor of History of Religions, University of Chicago
He wrote many books about religion
He studied in India, Univesity of Calcutta, with Professor Surendranath Dasgupta.
He lived for years and studied with Swami Sivananda in his ashram
He practised yoga for years, in the caves, together with other yogis.
I remember one of his books, in which he describes his out of body experience with yoga.
If you want more info, you can just search the Internet.