I see no difference.
^^^I think Cotard's is more a paranoid delusion, where that belief is very strongly held and possibly unshakable. Our ability to separate the feeling of not existing from actually fully believing that we don't exist would be the key difference here, I imagine.
Which actually comes from something by Simeon and Abugel apparently, most likely Feeling Unreal.Although the disorder is an alteration in the subjective experience of reality, it is not a form of psychosis, as the person is able to distinguish between his own internal experiences and the objective reality of the outside world. During episodic and continuous depersonalization, the person can distinguish between reality and fantasy. In other words, the grasp on reality remains stable at all times.