This is a rough draft only!
Iron Man/Captain American movieverse, light Tony/Steve in that they're sharing a bed and no one's wearing a shirt, but it's Steve and Tony Stark (and do we really want them to?). Tony's not sleeping well, and Steve doesn't do well being startled out of sleep.
The first time it happened, it scared the hell out of Steve. He'd been sleeping deeper than usual, serum did that sometimes, when it had been a while since he'd gotten good sleep, but it meant he hadn't noticed Tony starting to get restless.
Tony had three sleep settings, that Steve had noticed: insominia, dead to the world or restless that shifted to insomnia after Steve woke him up. Tony had asked him once to do that if he noticed it, and usually he did and Tony worked off whatever was bothering him and came back to bed or didn't, depending on what was going on and everyone was fine.
Tonight, the restlessness wasn't caught and Steve was in a deep sleep for once until the scream beside him jolted him up and then off the bed in a tangle of sheets and he groped for the lights and he groped for his shield, and only remembered at the last second that Jarvis controled the former.
The lights flooded back on without his assistance anyway and Tony was sitting up now, not visually hurt at all, blinking in the sudden light and turned to look at him. Steve supposed he must make an odd sight, in his Captain America boxer shorts that Tony insisted he wear sometimes, and no shirt, gripping his shield with the sheets tangled around his hips and legs. It would certainly explain Tony's expression shifting to vaguely amused.
"Might wanna put something else on if you're going off to fight crime," Tony yawned, and the words came out in that easy laid back way Tony usually had, but there was a tightness around his eyes and his hand was on his reactor in a way that Steve was pretty sure wasn't intentional. He didn't usually sleep without a shirt, even though the reactor didn't bother Steve much except maybe when they shifted in a way that the light was in his eyes, and really nobody could sleep with that bright of a nightlight, right?
Steve swept the room one last time for any threats, just in case, and then slowly lowered the shield and climbed back into bed. The lights dimmed, but didn't go off entirely, and he watched Tony visibly relax back into the pillows. Steve hesitated, and Tony waved a hand.
"Just a nightmare, it's cool, just.. go back to sleep, okay?"
"Are you..?" Steve waited for his brain to fill in the appropriate remark but it was being a little slow in cooperating.
"Cool? Handsome? A super genius?"
"Egotistic?" Steve grumbled with a smile and Tony gave a half grin that faded slowly.
"I'm even going to go back to sleep now, I think, so just ...don't make a big deal, or anything, okay?" Tony rolled over, away from Steve in a way he didn't often. Steve considered that, and shifted so he was curled up against Tony's back and could feel Tony relax the rest of the way.
"Okay." He had things he'd rather approach in the daylight too.
The lights went back out, and the two went back to sleep.