Obliviopsychosis

Obliviopsychosis is a life-threatening mental disorder whose incidence is so rare that it is unknown by almost everyone. However, it is known to the Oblivion Guard, those who practice Eldritch art, those who are part-Ultimordian, and anyone unfortunate enough to come across anything Eldritch.
It is caused by the acquisition of Eldritch knowledge in any form including but not limited to visual or text form, and a negative reaction due to incomprehensibility of Eldritch concepts to most lifeforms, which most definitely cause self-destructive instincts, brain damage and even gradual brain death. Effects vary, but the most common symptoms include permanent migraines, insanity, catatonia, and intense self-harming urges. The logical conclusions are death, insanity, catatonia, and dementia. Some lose their complete sense of self over time. The conditions of most of those who survive are haunting, to say the least.