That's a complicated question. As long as you are in faith to your tradition, you are always safe-including in a Sacred Sleep practice. On the other hand, if you have fears that this may happen you can attract that experience no matter what your tradition or practice. Most Buddhists traditions are of the belief that your karma (habits of mind) are what reincarnate. During Sacred Sleep practices you are recognizing that all is a display of the mind-there is no separation between mind and body. Christian/Muslims/Jewish traditions version would be that at death your Soul goes somewhere (up or down :). The Shamans practice "Soul Retrieval" as in a portion of your being has left and needs recovering. Others practice Out-of-Body travel experiences where it "seems" you are traveling physically (or non-physically) in the actual world or even other realms.