Been a few months since anyone replied to this, but I thought I'd add my own experience to possibly help others out a bit.
I read further up that ragdoll force can cause this issue. I was going to uninstall it just to get into the game, then thought about all the mods that depend on it, so decided to take a look at my load order before I bothered uninstalling.
Somehow, all the ESPs from the ragdoll mod were activated! I just unticked all except "realistic" and it fixed it
Hope that helps others with the issue.