You had fallen ill with a sickness called the ‘Soul Sickness’ after being consumed by despair shortly after your timeline was destroyed and you and your loved ones fell into SoulTown within The Silver Void, and were all admitted to the Soulful Hospital.

“It appears you have The Soul Sickness, meaning your Soul is not only consumed by despair and appears a very dark purple shade for now, but you’re also very sickly and weak…” Dr. Gaster said. “I am Dr. WingDing Gaster, I shall care for you.”