I think Silva knew he was hurt and was just screwing with him since he didn;t throw in the towel right away.
As for Forrest flailing on the ground, I think he kept going down "so easy" in order to try and lure Silva into a ground exchange. Forrest knew he couldn't stand up with him any more in his "hurt" condition. Aside from that, anyone that says Forrest was dropping too easily, TRY to work through the pain of an injury let alone have someone jabbing at you.