Sleep talking could potentially be a manifestation of negative energies, especially if it comes in conjunction with night terrors or if the contents of the talk are negative. Keep in mind, however, that if you are processing repressed thoughts or emotions, you need to work through them. The repression itself is what is truly negative, not the contents of your unconscious mind. As far as negative entities go, there are steps you can take to protect yourself in the spirit world. Try sleeping with a protective crystals like black tourmaline under your pillow.