The phrase "be a shadow/ghost of your former self" means to be diminished or lowered in quality, ability, or spirit. There are several synonyms that can be used to express this sentiment. One is "a shell of your former self," which suggests a loss of vitality and substance. Another is "faded glory," which implies a diminishing of past achievements or glory. "A mere shadow," conveys a similar idea of being a diminished version of oneself. "A pale reflection," expresses a diminished likeness or image of the former self. Lastly, "a shadow of your former greatness" suggests a loss of greatness or achievements. All these synonyms express the idea of being a diminished form of oneself from a previous state of being.