The Return of the Repressed.

This phrase is used to describe when bad memories and/or feelings of negativity are repressed in your unconscious mind for a while, they are bottled up and can come to the surface when triggered by something traumatic, frightening or similar to the bad memory.

Example: If you were attacked as a child and because it was traumatic you pushed it to the back of your mind and blanked it and forgot about it, then say someone close to you is attacked that can make the repressed memory return with unpleasant effects.