What mental illness does The Equalizer have?

I'm curious, in the context of the film "The Equalizer," what specific mental illness is portrayed by the main character? Is it a condition that is clearly diagnosed and addressed within the storyline, or is it more of a subtle hint or allusion to a deeper psychological struggle? Given the character's background and the events that unfold throughout the movie, could you speculate on how such a mental illness might have influenced his actions and motivations? Additionally, does the portrayal of this mental illness contribute to the overall themes and message of the film?