Two quotes came together here, one canon and one not.
Last year, broke my foot, laid up for two months, from 5x04, "The End". And Painful experience had established that Cas was still just angel enough that he couldn't catch Croatoan, from Misato's "Some Things to Hold Tight".
Timeline: Fall of 2012, Sam says yes and the angels leave; Castiel loses his angelic nature. This is late January 2013. "The End" takes place in fall of 2014.
So, spoilers ahoy through 5x04, and you have to wonder what kind of experience, exactly…
Castiel had gotten separated from the others pretty much through overconfidence. Even now, four months later, he kept reaching for his Grace and being surprised when it wasn't there; when he wasn't actively reaching, he tended to forget that he couldn't. So it hadn't seemed to be such a problem when he'd spotted an out from the mass of croats that also took him away from Dean and Jared and the others who were on the supply-raid-turned-ambush. He'd just taken it, fast, and it wasn't until he heard Dean shout Cas! behind him that it occurred to him that this wasn't a great idea. And by then it was too late.
Castiel had held his own for a little while; he wasn't an angel anymore (and he can't think too hard about that feeling, of his Grace slipping away like water through grasping fingers) but at least he could shoot (after more-or-less patient lessons from Dean). His initial plan had been to get around the croats and provide support for the others, but that turned into just running all too quickly, in an attempt to get out of the hospital and back to the vehicles.
Two croats jumped him as he inched through the hospital hallway, trying not to breathe too loudly, at least, since ceasing to breathe was no longer an option. He heard the one coming and spun to meet it just in time. He spent his last bullet on it, a solid hit but not one that would slow a croat down until the blood loss got bad, and then it was on him and they went over backwards on the linoleum, Castiel with his hands around its throat to keep the teeth away while it shrieked and raved and clawed at him. It bled on him, of course, but not anywhere near his face where he'd risk getting the blood into his system.
And just when he was starting to think it was weakening, that the blood loss was getting to it, he realized that there was someone else coming down the hallway, and a quick glance confirmed it wasn't any of his friends. He closed his eyes for a second to gather his strength—reached for his Grace, flailed for a moment when it wasn't there—and threw the croat off, trying to aim it at the other. He scrambled to his feet as the two infected collided and recovered their balance.
He remembered to grab his gun, at least. Being out of ammo now didn't render the weapon useless in the future; they'd all learned that lesson quite well the time Dean put some kid on bread and water for leaving an empty rifle behind.
Castiel backed down the hall as the croats advanced on him. He tested the first door but it was stuck or locked; the second one yielded to pressure and he ducked through it and slammed it behind him. The croats ran headlong into the door and it jumped open a few inches before he managed to shove it closed again. He leaned on it hard.
The room didn't look like the kind patients slept in; there was a high table rather than a bed, and counters with cabinets over them—and a window. A window with a little metal balcony outside. Castiel took a deep breath. He'd all but trapped himself in here, once again counting on something he didn't have; not so long ago, he could have simply flown out of any dead end and something in his head thought he still could. But the balcony, the fire escape he thought, offered a way out.
Against his back, the door shuddered. Dean had told him once that the original victims of the Croatoan virus had been able to think and plan, but "these new ones, they're like frickin' zombies." Castiel wasn't honestly sure what a zombie meant in this context, but the modern-day croat was all straightforward aggression. At least that made them predictable.
The problem was that Castiel's own body was the only thing keeping the door closed, and that wouldn't last forever. And he was going to need at least a few seconds to get out the window. The door had no lock, not even a wire hook and eye. Castiel closed his eyes and thought hard.
The plan he came up with wasn't anything great, but it was what he had so he opened his eyes and got going. The padded table wasn't quite within reach, but there was a chair next to the door and he slid it until he could use it as a spacer; then he could grab the table, though the angle was awkward. A minute of rearranging, and one heartstopping moment when the croats managed to coordinate their blows, later, the table was up against the door, the chair was against the table, and Castiel was within arms' reach of the window. He was right in front of the cabinets, and since the purpose of this whole business had been to gather medical supplies he opened the doors for a quick survey.
The shelves were fairly full, so he went through the acrobatics necessary to take his pack off while keeping at least one hand on his doorstop, then stuffed the pack full of everything that looked like a medication. When he shrugged it back on, he was wearily surprised by how heavy it felt. Angels didn't care about such mundane concepts as weight.
That done, he turned his attention to the window. It had a simple mechanical latch and hinges at the top; the pane swung in, which was going to make things more exciting. He popped the latch and pulled in and up. And stood there for a few seconds, trying desperately to get his heart under control. It didn't work, but he had to move sometime.
Castiel waited until he heard the thud of a croat hitting the door before he moved, sliding out the window as fast and smooth as he could. Behind him the table scraped over the floor as the croats pushed the door open at last. His heart pounded in his throat, but he made himself lower the window smoothly instead of just letting it crash, because breaking it would take them a few extra seconds.
He was only on the third floor. The first ladder went smoothly enough. The second, the one that swung down, ground to a screeching halt when it wasn't quite extended, but he didn't really have time to argue with it; above him he could hear the croats pounding on the glass. So Castiel was most of the way down the steep, narrow stairs when the rust let go under his weight; the drop was only six inches or so, but he was completely unprepared. He teetered and fell. His right boot slipped, then caught in the rail that held the stair tread and his foot twisted as his body fell out of alignment. He landed on his back with a bonejarring slam that did nothing to distract him from the sudden blossom of pain in his foot. He was sure he could hear the bone cracking, or maybe it was bones.
And above him the window shattered at last. Glass fell towards him, glittering, strangely beautiful, and it didn't occur to him till it was almost too late to throw his arms over his face. Only a few pieces hit him.
He could hear someone descending the fire escape. He thought it was only one of them, but he couldn't make himself take his arms away from his face to check. It didn't matter anyway; he couldn't run, his gun was empty, and no matter how many croats there were he was going to die. Hidden in the darkness under his arms, Castiel closed his eyes as if that would save him.
The fire escape screeched again as the croat stepped onto it. Castiel's descent had broken the seal of rust that had been his undoing, so the ladder clanged to the ground. He heard the croat's unsteady steps, then a pause, and then it must have jumped because weight came down on his broken foot and he heard himself make a sound that was all inhale and fire exploded before his eyes.
He was waiting for the next thing, for a hand wrapped in his shirt-front or for the croat to simply start kicking him, when he heard a shout. It was nothing with words, but he knew that voice, Dean's voice, as well as he knew his own. And then there was a shot, close, and the croat fell on him bonelessly. A few of the shards of glass dug into his chest; Castiel knew there was something to be concerned about there but he couldn't remember what.
It took him a moment to coordinate enough to think about pushing the body off, and he had just started to make a serious effort at it when Dean dropped to his knees beside him.
"Cas, you alive?" Dean demanded. Dean did a lot of demanding and ordering these days, since Sam had…been lost. Castiel rolled his head enough to meet Dean's eyes and said, "My foot is broken."
"How much of the blood is yours?" Dean asked, as they pushed the dead croat the rest of the way off.
"All the croats," Castiel said, and even then he could feel gratified at the flash of relief that went over Dean's face. "Don't get any in your eyes," Dean said.
"I'd almost think you care what happens to me," Castiel said, trying to joke to distract himself. The pain in his foot was nauseating, or at least he assumed this was nausea.
"Yeah, well, don't get used to it," Dean said. "We gotta go. We cleared 'em out for now but the lookouts have a big group on the way." He helped Castiel sit up and waved Genevieve over to take his other side. The three of them got Castiel to his feet in fairly short order, and then it was a matter of not vomiting or passing out on the painful trip to the nearest jeep. Everyone piled into the vehicles. Castiel was surprised and pleased when Dean stayed in the jeep's bed with him.
"Check my pack," he said as they started to move. "I filled it up after we got separated." He could hear the tightness in his own voice, from the pain.
"Separated, is that what you call it when you run away in the middle of a fight?"
Castiel closed his eyes so he wouldn't have to watch Dean look angry at him. "It was a mistake. I was counting on…" and he didn't know how to finish that sentence. On his lost Grace, on his own abilities, on Dean; he'd been counting on something that wasn't there anymore. He leaned forwards enough for Dean to slip his pack off his back, then settled against the side of the jeep's bed again. The ride was rough and every bump jolted pain from his foot.
"Yeah, fine," Dean said. He unzipped the pack and rummaged through it, and after a second produced a small, grim smile. "But hey, at least you found some of the good stuff," he said, and rattled a bottle significantly. "Oxycodone. You're gonna like it."
Castiel tilted his head in confusion, and didn't understand why Dean looked away. Dean screwed the top off the bottle and shook a pill out. He handed it over. "Can you swallow that dry?"
"I don't know," Castiel said honestly. He turned the pill over in his fingers for a second before putting it into his mouth. It was chalky, and bitter, and he wanted to spit it out but Dean's eyes were on him so he swallowed it instead. "That tastes horrible," he said.
"In a few minutes you won't care," Dean replied shortly.
The ride back to camp was going to be long, but soon Castiel realized he didn't care. He felt strange, warm and almost as if he were floating. Or flying. He put out a hand, trying to get Dean's attention, and missed on the first two tries. "I can fly again," he said, or tried to say; he could tell the words weren't quite right, though it seemed Dean caught the drift of it from the grin he produced. There was little enough humor in it.
"You're stoned," Dean said. Castiel shook his head, because that wasn't the right word for this; this was soft and light and warm and stones were hard and cold and you could break something on them. "Yeah, you really are," Dean said, and Castiel wanted to explain but it was too much effort. The rest of the trip passed in a timeless haze.
Castiel came back to something resembling awareness when Dean started trying to pull him out of the jeep. Everyone who was hurt was hauled to the cabin they used as a clinic, so that the doctor could take a look at them; Kim was in the process of dying of cancer, but there wasn't anything they could do about that so he just kept working. Castiel didn't pay much attention while the man dealt with his foot, catching fragments of sentences like what's he on and stay off it for six weeks at least and said the blood isn't his. But when Kim opened up his ruined shirt, there was a silence with a quality that penetrated the fading warmth enough that Castiel realized he should pay attention to it.
Dean and Kim were staring at his chest, so he looked down at it as well. There was blood, now mostly dried, all over it, and gouges where the glass from the broken window had dug into his chest.
"When did you get the scrapes, Cas?" Dean asked quietly.
That was a dangerous question, Castiel knew it somehow, but the habit of answering Dean when he asked ran deep; he said, "When the croat fell on me. There was glass from the window." Dean looked away from him, his eyes wide and full of a pain that Castiel didn't quite understand.
Dean's hand moved to the small of his back. Castiel felt that twinge of warning again.
"How long did it take you to get back?" Kim asked suddenly.
"About three hours," Dean said, after a moment of calculation.
"If he was going to, he'd be showing symptoms by now," Kim said.
"The Oxy could be keeping them down," Dean replied, though he didn't sound like he wanted to believe what he was saying.
"So give it some time to wear off." Castiel didn't like the sound of that, if "wear off" meant he'd lose the warmth, the lightness. "We can keep an eye on him till he comes down."
"I'll watch him," Dean said, sounding grim. "You get back to the others."
They put him on a cot in the patient room, and Dean sat next to him on a folding stool, holding his gun between his hands like a touchstone. As the warmth of the drug faded, Castiel slowly realized what was going on; Dean was waiting for him to show symptoms of Croatoan, and when he did Dean would shoot him.
Except that he didn't. His foot began to hurt again, or at least he started caring again, and he lost the feeling of flying, but he didn't start to hyperventilate or spike a fever. And four hours after they'd gotten back to camp, Dean sighed and stood up, tucking his gun away again.
"When we first ran into it, I thought I was going to have to shoot Sam," he said, and even over his own pain Castiel could still hear Dean's, bitter and bright as it was any time he had to mention his brother. "Turned out he had enough of ol' Yellow-Eyes in him that he couldn't catch it. I guess that works for angels too."
"I'm not an angel," Castiel said, as if there could be any doubt; angels did not lie on cots, breathing hard around pain and wishing hard for something to make it stop. Angels could feel as if they were flying any time they liked. The angels were gone, and there was only Castiel now.
Only Cas.
"You're enough of one for this," Dean said. He pulled the bottle of Oxycodone out of his pocket and tossed it over. "Here. Try not to go through 'em too fast, I dunno when we'll get to stock up."
Cas looked down at the bottle and tried to count how many pills were in it; how often he'd be able to remember what it felt like to fly. He turned it over in his hands like Dean had turned his gun, and when he looked back up Dean was gone.
So, trust me: the first time you take opiates, they do hit you like a frigging truck. And Oxy's pretty heavy-duty.