This is actually a perfect set-up for a mercyvariant script I’ve had lying around for a while.
Gaster actually suspected early on that Papyrus might need glasses, but he never followed up on it for various reasons. As such Papyrus has just always assumed his bad vision is normal!
Dreams where you’re being tortured, dreams where you’re not being tortured, it never ends!
Sans isn’t actually dreamsharing with him here, but Papyrus has told him about this dream before, so he can guess. Can never remember who it was that was so important to him though…