Jim jumped with surprise when she started yelling at him, and when she got out of bed, he was out of the chair in the same instant, ready to catch her if she fell or tried to make a run for it. Which obviously she couldn't but he wouldn't put it past her to try and then hurt herself in the process.

When her knees gave out, he moved forward and pulled her into his arms, more or less manhandling her into a cuddle on the edge of the bed. Because it was the only thing he could think of to do. He knew about PTSD in theory but seeing it right in front of him wiped all of that Starfleet training out of his head.

So he didn't actually have anything to say in that moment. The only thing he could do was keep a tight, hopefully reassuring arm around her, and wipe away the tear tracks on her face with his other hand.