Though the Abyss is riddled with countless dangers and hazards, one of the greatest challenges facing delvers is, in fact, the ascent from it. This is due to a phenomenon called the Curse of the Abyss. The term refers to a series of symptoms that manifest upon ascending while inside the abyss, with its more scientific name being "Strains of Ascension". The effects of the curse manifest after ascending around 10 meters within the Abyss, and there's no way to avoid it through conventional means. The Curse affects all living things, however the creatures that inhabit the abyss have developed ways to sense its flow and avoid it.
The deeper one delves, the more severe the symptoms are, ranging from dizziness and nausea to intense pain throughout the body, loss of senses and even death. This makes the return trip from the Abyss extremely difficult, and it is not uncommon for delvers to perish on the way up. Particularly, the curse of the 6th Layer("loss of humanity or death") makes the return journey physically impossible for humans.
The curse results from piercing the force field of the Abyss while ascending, although this fact is not generally known. Therefore, areas where the force field is weaker also result in the effects of the curse being less severe. In certain specific places, like Nanachi's Hideout and The Village of Ilblu, the force field isn't present at all, and so the Curse doesn't occur either.
Birthday death disease
Birthday Death Disease is a strange disease that occurs on the surface, caused by an abyss curse. A lot of people died at the same day of the year they were born, has been called off as a rumor but in entirety it becomes true. Its symptoms usually starts with a high fever and forcibly becomes an unknown condition that cannot be treated by ordinary doctors. The victims of the disease is still counting in Orth.
However, there is evidence pointing to the force field as a possible cause of this illness, as it's revealed that once one is removed from Orth, the sickness vanishes, as if it were never present at all.
Faith in the abyss
A religion that was formed using the Abyss itself, and it appears to be a very common belief for those that delve into the Abyss. Instead believing in a God, those that turn to this religion believe in the Abyss itself. Because the bottom is unknown, it replaces their God and grants them hope in the after-life. It's based on the principle that if you lose your life within the Abyss, your soul will descend to the bottom and live as a form of spirit of the abyss. The unreachable depths of the pit makes people believe that it transcends life itself.
Curse of the abyssCurse level 1
Light Dizziness and NauseaCurse level 2
Heavy nausea, headache and numbness of limbsCurse level 3
Vertigo combined with visual and auditory hallucinationsCurse level 4
Intense Full-body pain, dizziness from pain and varying amounts of internal and external bleeding across the bodyCurse level 5
Complete sensory deprivation, confusion and self-harming behaviorCurse level 6
Loss of humanity or death, or very rarely, the BlessingCurse level 7
Certain deathCurse level 8