i think rick may have bipolar or some kind of split personality disorder hes developed in the apocalypse. i saw this because of his occasional "visions" if you wanna call them that where he talks with shane. shane talks to him and influences him and encourages him to do things a lot more violently and viciously, kind of like a devil on his shoulder.
Could be worse, could have been Patton Oswalt as "Happy".
That’s just PTSD.