the stress, pain, and PTSD from hiding in his own brother's dead body caused him to freak out and go bloodthirsty. he killed his dad in a fit of insanity. when he snapped back, he sat there, his father's sliced-open corpse laying in front of him. he started doubting his sanity and sat there, crying. he eventually got over it, but now every time he gets PTSD of that incident, he goes bloodthirsty again until snapped out of it.