In Response To The Askreddit Question

If I was going to pick a single thing, I guess it would have to be the one who came back.
I've been doing research for a personal project and I came across a listing for a traumatic brain injury group in my area. I recognized it as being the home of a young man who I'd recently come across in the news, and I reached out to see if I could meet with him. Since he's relatively cognizant and only suffers from physical issues and impulse problems, he's allowed to make his own decisions on things like this and after I told him who I was he agreed to meet with me on the condition that his mother could also be present.
We met in a coffee shop, per his request, and I bought him a black coffee that he dumped sugar into until his mother gently stopped him. She said very little through the entire visit, and appeared to be there solely for moral support. Occasionally he grabbed her hand or made child-like noises of discomfort and buried his misshapen head in her chest while she soothed him. His appearance was startling. The front of his forehead appeared to have been shaved cleanly off, and what remained was completely flat, and noticeably lower than the bone around it. Of course I wanted to ask why it hadn't been properly repaired but the chance never came up. Along with his forehead, the tip of his nose was also strange. It had been sewed back on, and the scar tissue had healed badly, giving it a bulbous, lumpy texture. His appearance combined with his strange vocal tics attracted attention but he didn't seem to notice. He was entirely focused on telling me his story.
He and his mother were hiking the AT for her 65th birthday, something they'd been planning on doing for years. The hike was going spectacularly, and they were making great time. I'm familiar with the section of trail they were on; it's incredibly remote, as much of the AT is, but the land is relatively flat and it's a great place for the less serious hikers. Prior to his incident, there were very little problems here.
One evening, they chose to camp off the trail rather than press on to the next shelter. They set up camp about ten yards from the trail and went to sleep shortly after dinner. At some point in the night, he told me, something woke him up. As he sat up in his bag, he had the sense that whatever it was had just ended. The air had a strange vibration to it and he had a distinctly uneasy feeling that something was nearby. Exiting the tent, he remembered being suddenly overwhelmed by a feeling he had trouble describing. Whether due to his injury or genuine loss for words, he struggled and became frustrated until his mother reminded him of how he'd described it to her. Holding him against her chest, she explained that before being packed up and whisked away by Life Flight he had told her it was like being wrapped in a warm, thick blanket. It was a deliriously calming feeling, and when he found himself moving deeper into the forest he wasn't afraid. Picking up from there, he recalled only patches of the walk. He remembered stepping on something, a twig as it turned out, and feeling it spear into his foot, but there was no pain so he kept going.
He seemed hesitant to describe what he found after an undetermined time but I didn't need him to explain because I already knew. He described them as being from his childhood home in the Smokys. When he began climbing them, the third step squeaked just as it had back then. His narrative became jumbled here, as he tried to explain what happened next, but from what I could piece together this is what he saw:
As he reached the top, he found himself instantly and bafflingly back on the trail, but although he recognized where he was, something was very wrong. As he described it, there was something wrong with the light. As if the air was full of smoke, giving the light an eerie orange quality. But there was no smell of burning, no heat, and the air was clear. When he looked at the sky, here too he sensed something horribly unfamiliar. He sensed a great chasm behind the sky, as if the clouds were only painted onto a false ceiling suspended above the earth. He made a reference to 'that smart rat in the maze, with the man', which I've interpreted as a comparison to the titular mouse from Flowers for Algernon. Somehow, he had gone somewhere and had found himself here, where he'd began but somehow infinite distances away. When he screamed the sound came from behind him.
He does not remember how he got out, or how much time he spent in that place, but he suspects that it was a substantial amount. Lifetimes. Millennia. He does not feel the same person that he was before he left. When he was found at the edge of camp, he was unconscious and bleeding heavily. The ridge of his forehead and the tip of his nose were gone, as if shaved away by a laser. The pieces were never found. In recovery, his brain damage became evident, and after considerable attempts were made to reverse it he was placed in the TBI home, where he has lived ever since.
I've stayed in contact with him and his story has never changed. As of now, he's the only person I've been able to talk to who knows where they go.