When Tony suddenly stopped and began to hyperventilate, Steve stared at him for only a moment before he realized what was going on. Though PTSD had been poorly understood in his time, his association with Sam and a lot of time on his hands worrying about what was wrong with Bucky had caused him to turn to books on psychology. And he'd quickly learned what shellshock really was and what to do about it.

He turned to Tony, shifting the suit on his shoulders just enough to free one hand. He wouldn't be able to hold it long like this, but he put his free hand on Tony's shoulder, hoping to give him something to distract him from his fear.

"Hey, Tony," he said in a quiet tone. "Just relax, soldier. You're gonna be just fine."