>>7193I think it's a combination of the weird psychedelic imagery on top of the sequence of Joker on the train, with all his friends moving around him, laughing, talking, and joking. It kind of encapsulates the feeling of time flowing around you, like being a plank of wood stuck in a creek, while everything goes on and you're left in the dark; it kind of links back to the weird nightmares I had. I hope that what I'm saying makes sense.
Speaking of DELTARUNE, when I first played the game, I almost thought that it was some kind of… post-apocalyptic scenario? That's kind of the wrong way to put it. It felt like a lazy parallel world (danganronpa reference?); the small-town businesses were replaced with a shitty pizza joint, Undyne and Alphys never met, Mettaton never got his body… Obviously, the quality of life for the townspeople was better than undertale, but there just seemed to be something "off" with the whole thing.
I've never really had this experience so I might just be talking out of my ass, but I imagine it's kind of like remembering some happy time, with a repressed trauma lurking somewhere in the recesses of your mind. Little things are off, and they add up to something bad, but you don't know what.