Collision glitch

In chapter 5 at some point after saving my game, around the point where you're looking for the liquid nitrogen, I started being able to walk through doors. Closed ones. And then items I found in lockers or chests started instantly falling through the floor before I could grab them. And then collision with any enemies turned off, including when shooting them. AND THEN enemies started not loading in any of their removable parts, which means they're just floating torsos and thighs. Now completely impossible to progress as I can't really interact with anything, and even when I lure the Hunter's, uh, pelvis...into the cyro freeze chamber, the game doesn't recognize it, just says the chamber is empty. So I gave up and moved through the next locked door without completing that, and eventually found benson's rig but the game doesn't recognize I have it, Nicole's hologram doesn't load in...my whole save file is just fried. Frustrating.