I am desperately looking for this book?

it is a teenage fiction book, not unlike a judy blume adolescent book, about a girl who learns how to astrally project herself? ( i think 1980's) at the end her body becomes inhabited by another soul, and she roams around without her body until she finally reclaims it! i want to buy this off ebay, but can't think of the title or author? i would be eternally grateful!