Based on some creepypastas and on a site called 'SOMETHING IS GOING ON' that was mentioned in 4chan's case, 'I am God'. This story is a little bit based too in this 4chan case.
Sans was sobbing a lot. The death of his father was something that hit him like a punch on the stomach.
He was thinking of going to a medic on the next week because of intrusive thoughts and wanting to kill himself. He even ended on a hospital for cutting his skin until it bleed and he passed out.
He had a dream before going to medic.
The dream had Undyne, Papyrus, Asgore and Toriel.
All they said were 'No'.
A knife was on the floor, full of blood.
"Fuck the whore" Papyrus said while strangling Undyne.
"We all die." Alphys said.
Everyone stared at Sans.
"I HATE YOU." They all said.
Toriel cut her wrist and throw the blood on the corpse of Undyne's arm.