Everything was going as planned. They figured out what was in the lake, they had the necessary equipment, and it was gonna be an easy hunt. Just kill one small lake monster and be done with it. Until one small lake monster turned into seven lake monsters who were bigger than even Sam.
Sam who was currently trying to fend one of them off by jabbing a spear through its middle, when one suddenly comes up behind him and grabs him with its four giant arms, dragging him into and under the water before he could so much as breathe.
Vaguely, he knew he should be hearing Dean's muffled shouts of 'Sammy!' But right now, he couldn't hear anything past the rush of water, the pounding of his heart, the laugh of the creature that was holding him as he carried him down, down further into the depths of the lake. Sam always thought that the depths of a lake would be beautiful, that you'd be able to see sights and colors you'd never see otherwise. But in reality, it was just dark, blank, inky nothingness that pulled at Sam until he couldn't tell if his eyes were open or shut. Then, just as suddenly as he'd been plunged into darkness, light came and filled every last crevice it could find.
It was so bright it lit Sam up from the inside, lit him on fire and burnt him until he couldn't take it and he shut his eyes, but that didn't help at all. He heard an ungodly noise before he succumbed to the will of the water, and the world went dark again.
He wasn't expecting to wake up. As soon as he was conscious, he opened his eyes to see Gabriel, hovering over him with his hands on his chest and a manic look on his face. Sam watched him for a moment, but Gabriel wasn't looking at Sam's face; rather, he was concentrated on Sam's chest and stomach. He made a soft noise, forcing Gabriel's eyes to refocus onto his. He smiled slightly, it being all he could do right now, but it had the desired effect and Gabriel sagged in relief.
He raised his hand and placed it gently on Sam's cheek. "Never do that again, kiddo. I don't know what I'd have done with myself if I hadn't shown up in time."
Sam wanted to promise that he wouldn't, but he couldn't find it in him to make promises he knew he couldn't keep.