Jim hasn't realized yet that he's physically acting out the memories. When he was trying to stop Austin, he doesn't know how he got on the floor, assuming that the other man took him down while he was incapacitated. And this last one didn't have him moving too far, not enough that he's put it together.

"Hurt? They're just memories... aren't they?" He can't get hurt by something in his own head, right? No matter how awful they are, they can't injure him, or he'd have to worry about radiation sickness.