I remember Yoga being really popular in the 1980's.
It was!  I remember that too.
Apparently it dates back to the 6th and 5th centuries BCE, coming from India during the pre-Vedic period.
Yes, I have researched India for a historical society I was in. 
Do you have any idea how it ties into the early history of India?
It's been awhile since I researched it, but I do know that it was developed that early in history.  It was interesting to read about it!
I guess the modern derivative of the ancient practice dates as far back as the first millennium CE, but has only real caught on around here this century.