become a shadow of (someone's or something's) former self

To become dramatically less healthy, vivacious, or robust, often due to negative circumstances. Sharon has become a shadow of her former self after battling such an aggressive disease for so long. This town became a shadow of its former self after so many local businesses closed down. Tom's become a shadow of his former self since the accident. His bubbly and outgoing personality has been replaced by gloom and seriousness.