A/N: If you've gotten this far, I assume you've read the tags and summary. Seriously, triggers ahead. This is a story about triggers. Please do not read if you struggle with self harm or mental illness.
Sam started hurting himself after Leviathon.
After the hallucinations of Lucifer stopped and the cut on his hand healed, Dean and Bobby pretty much forgot about his stay 'round the bend (except when they argued over who did the messy jobs- then Dean would dredge up his questionable mental state again). But sometimes, even now, Sam wasn't sure whether he was seeing double, or the real thing, or curled in the safe room of Bobby's old house. He couldn't ask Dean, or Bobby, or anyone, really. If he was hallucinating, how would anyone in it be able to tell him otherwise?
So he'd go into the bathroom of their current motel, run the bath water till it was hot. Dean always assumed he was just doing what guys do, and left him in there while he fed the vibrating bed all his change (seriously, the guy had a problem). Not long, but long enough that he could strip off his pants and sharpen the knife.
It was always Ruby's demon knife, just for sentiment's sake. He'd sit on the edge of the tub with his feet in the bath water and carve shapes into his thighs. At first they were triangles, like the first cut on his hand, but then he began to branch out. Warding symbols to keep angels out (no consent would let them in now), devils traps to bind them in (he supposed his tattoo made those obsolete), Enokian words to protect against Cupids and their marks, slicing through his skin on a demon's knife, forged with angel blood, charged to kill. He supposed if it stung a bit more, well, he had demon blood in him, didn't he. Then he'd grit his teeth, run it under the scalding water, wrap it in one of their copious rags, and dress again.
He never wore shorts -too vulnerable in a fight- so Dean never knew. And whenever he suspected that the world wasn't right, until the wounds faded and scarred over and healed, he was able to grip his thighs till his knuckles turned white, relishing the pain that told him he was alive and chased away the monsters of his mind.