Peter obviously wasn't going to surrender without a fight. After sensing the Venom Symbiote's intentions, he concentrated most of his effort on his brain, stubbornly defending this most crucial area. That was also why, from Iron Man's perspective, his body seemed to be continuously going berserk. But in reality, his condition was gradually improving! Aside from the fact that his body was basically beyond his control, his consciousness was becoming clearer and clearer instead. The headache he had felt earlier was also gradually fading.