Sans:
The pain in his skull is still there. The searing sensation was like nothing he'd ever felt before. His head ached for such a length, that it started to make the skeleton feel distant, lost in his own surroundings, lost to the thundering ache building up near his temporal bones. The more he tried to think, the more everything around him felt eerily unfamiliar, the shock of his surroundings had him panicking at random intervals, his composure not very used to being broken. The town he had spent the last few years in was alien to him. He was a stranger, an outsider, this feeling was not new. He noticed the more the days went on, the more pain built itself up. It had started about a month ago, right around the anniversary. The headaches, the feeling of separation. Some semi-familiar monster on the street would give him a strange look sometimes, but he rarely crossed the streets anyway. So he did well ignoring those sidelong glances, and the curious or concerned ones that sometimes strayed around his sentry station.
The icy crisp air whirled around him, drawing quicker breaths that swirled visibly past his teeth. The poor air quality, and the chill were more pronounced than usual. Though his body was not usually prone to such things, the wind wisped right through him today, causing his whole body to shake and tremble. The raw air made him wheeze. It was freezing. The only explanation Sans could assign to the way his body was rattling, the way the pain was growing in the back of his skull, but he was starting to doubt it.
Sans shivered, it settled in his ribcage and creeped up his vertebra. He let out a few quick breaths of distress and confusion, panic overtaking his pain-addled mind. They billowed out in a steady stream, dissipating before more could take their place. A sharp pain tore through the base of his skull, sudden and jarring, leaving the skeleton reeling. Sans's breath darted out of him now, coming in sharp gasps that he could no longer control. The world is collapsing, the world is collapsing on me! His hearing became mute with static that danced across his vision, clogging his senses with white noise. He could scream, but the noise wouldn't register. He couldn't even tell if his scream had erupted through the foggy deafness.
Cold wet slush pressed against his knees and hands, the only indication to him he had fallen over. He could feel hard boney fingers scratching against his skull, willing the torment to stop, he didn't know whom the fingers belonged to, they felt disconnected. The phalanges dug and scrambled helplessly, the pain the action should have caused drowned out by the intense pressure flooding his skull.
He didn't know how long it took for the fog to let up, it left him in such a daze he hardly remembered. He couldn't recall when he'd transitioned from curling up on himself, to laying spread across the snow. His chest heaved, he watched as it extended and contracted, a dull throbbing rang through his mind as an aftershock, toll-toll-tolling as he tried to focus on the gentle sound of the river flowing.