Technically a form of Mana Poisoning, Tràyalià's Sleep slows down a persons thoughts and eventually places them into a sleep that they will never wake up from.
The condition is caused by a person entering an Ambient Magic field composed mostly of Ether magic. Ether magic is a magic of stability, and the magic usually sees the constant growth and change of the body as a detriment. If the magic first gets into the organs and limbs, the case can treated as Mana Poisoning. Tràyalià's Sleep is only when the mana enters the brain first.
At first, the only sign is a slowing of thoughts, subtle and insidious. Over the coming weeks, the inflicted will get more and tired, sleeping often. Eventually if untreated, the victim will fall asleep, never to awaken again. Their body will never age, and never change after that. The body exhibits traits like pure magic crystal, and is near as hard to damage.
The only prevention is staying away from high density ether magic. If someone has to go it, they should wear a helmet of Mythril to keep the magic out. When camping, they should combine that with an array of mawàmortu crystal to keep the camp clear of ether.
While most fear it, a few see the ending sleep as a form of immortality and will intentionally induce the symptoms when close to death.