Where mind and body intersect in disease
Soul Sickness is an extremely serious condition stemming from mental-health issues causing a corruption in a Sophont's soul and meta. Given the proliferation of psychological warfare and the usage of Auric Immolation in the battlefield, it is not as rare of a condition as would be desired.
Soul Sickness is caused by a Sophont undergoing enough duress that the combined weight of their mental illnesses pushes their soul to a tipping point and their soul begins to putrefy.
Sophont affected by Soul Sickness produce Selschaeus (Dark Unity) in and around their bodies. Their homes often become coated in a thick grime of Dark Unity and it will begin to appear as cysts within their body or dripping from their pores and orifices. Other symptoms include an exacerbation of their mental illnesses as their brain and soul engage in a negative feedback loop, which in turn can trigger a full variety of physical symptoms as their body reacts to the stress and to the foreign-body presence of the Dark Unity in their body. It is not uncommon for sufferers to die of a Dark Unity-coated bloodclot.
Keep the patient in the presence of a Meta Purifier or keep them in an Meta Void so that their soul stops putrefying and exacerbating their physical and mental situation. Put the patient under intensive care for their mental state.
The affected will end up in a ghoul-like state, body sustained by Dark Unity and becoming increasingly monstrous until they become an Abomination, or die. Someone with a critical state of Soul Sickness poses a threat to their entire community.
Soul Sickness exacerbates all conditions—mental and physical.
Due to the presence of Soul Sickness, society takes mental health issues extremely seriously. Early on, it was understood that pain and suffering could cause Soul Sickness, but it wasn't until the advanced stages of the psychological sciences that people began to understand what mental illness was, what caused it, its relationship with Soul Sickness, and how to treat it. Soul Sickness is a horrifying condition to develop, and is the sort of thing that people are always looking over their proverbial shoulder for.