He is possessed, and the reason for that is because he is weak willed. Being possessed is in fact a refelction of a weak will, because the will itself is something you decide on, or choose yourself, because you rationally believe it is right.

Ralph just acts like a raving lunatic. There is no sign of any conscious decision on his part. He is just acting in reaction to the trauma he received from the incident.

I think he was mentally damaged from that, so I guess the issue of him being weak willed NOW is no longer relevant.