To dream that you are a slave suggests that you are not taking charge of your own life. You may be a slave to your job, to your family, to some habit, or to some obsession. In particular, to dream that you are a sex slave implies that you are too submissive when it comes to sex. Perhaps you need to take more of an initiative or be more dominant.
To free slaves in your dream implies that you are liberating an aspect of yourself that you have been suppressing or that you have previously not expressed.