Immortality fatigue is a mental condition unique to a select few- Omnia and other immortals who were not born as such. It's thought that due to not having been immortal since birth, those with such a form of immortality suffer consequences as a result of not being properly adapted to live such long lives. The general consensus of the condition is that those afflicted by it are suffering the effects of having lived so long that their brain function has become altered and struggling to adapt to having retained so much information, such as memories, over their extended lives, that it begins causing issues for them. The condition while already rare, is extraordinarily rare in omnia who have been such since birth, and most often those within such group diagnosed with the condition are often re-diagnosed later on for other similar yet still distinct issues.
Immortality fatigue presents with a wide array of symptoms, the vast majority of them affecting the individual's mental state and activity. Long term memory loss is by far the most common symptom, especially in immortals who have vastly outlived their ordinary lifespan, and also one of the earliest to make itself known. The long term memory loss often can be confused for dementia, but differs in that those with immortality fatigue do not lose their sense of self, awareness, or mentally deteriorate at an exponential rate, nor suffer other symptoms of dementia. Rather, long term memories become harder and harder for those afflicted to recall and the longer ago the memory, the more likely it is for the sufferer to have forgotten it. Generally, immortals with the condition will still be able to remember important events or memories, such as major historical events and things that personally affected them, but cannot recall vast amounts of time spent in the mundane. The memory loss seems to be selective, not on the victim's part, but in what is lost. Extremely severe cases may see immortals who have lost the ability to recall decades or centuries of time at all and all events within that timeframe, including but not limited to major historical events, personal trauma, life events such as births and deaths, and friendships gained or lost. Short term memory loss is a much rarer symptom, but often associated with severe cases of immortality fatigue. Short term memory losses are often attributed to a mix up in the mental state where in the immortal is unable to place themselves in time and may begin to act out routines they may have abandoned for decades or even centuries. This is not associated with a lack of awareness or confusion such as that found in dementia patients, as the immortal still retains clarity, but rather a form of trying to 'fill in the blanks' when they have forgotten their new daily routines, and pick up routines they may have held in the past. Short term memory loss associated with the condition also includes an inability to distinguish time properly, where in those afflicted will often have 'gaps' where they do not remember what they have done that day, lost track of large swaths of time, and cannot recall the day, month, or year it currently is, but still remain lucid. Often, these memories do return at a later date but cannot be accessed until moved into long term memory. Suicidal thoughts and ideations along with depression are also attributed to the condition. A lack of a natural lifespan as expected is thought to be the main contributor to this, as most immortals not born such often had a period in their lives where in they expected to one day die. It's thought that grief is also a major contributing factor, as most immortals will eventually outlive far more of their close companions than the average mortal, and as immortality is a rare and more often than not a trait that cannot be passed down, immortal will often outlive all of their relatives, including their own children. Most immortals however do not view their suicidal thoughts or ideations as a bad trait or as distressing, but a logical sequence of events, often still holding onto ideals that anything that lives should one day die. This ideal is often missing in those who were born immortal. Generally, these immortals rather view it as a kinder option, in that they get to choose when, where, and how they will pass on. Depression, however, is a much more distressing symptom that most with the condition often seek to alleviate. It's estimated that around 62% of unnatural immortals will suffer depression at some point in their lives, and 48% of those will medicate for it. Often, addictions are in close association with depression in immortals. Alcoholism and narcotic dependencies are much more likely in unnatural immortals than the general mortal or born immortal populace. Both depression and the addictions associated with it in immortality fatigue are thought largely by immortals to be a symptom of boredom, as due to their long lives, their experiences become incredibly vast and those not suffering from major memory loss often begin to have a much harder time in finding joy in live or things to entertain themselves, turning to more and more extreme behavior. Those that cannot fulfill their needs to be mentally stimulated often become violently depressed and may turn to alcohol and drugs out of desperation. A much smaller percentage develop gambling addictions. These symptoms often tend to subside with proper medication, therapy, and being given long term goals.
There is no true treatment for immortality fatigue, instead only treating it's symptoms. Immortals who develop immortality fatigue often state that it can come in cycles, with most symptoms becoming absent for long periods of time, up to centuries, before reappearing once again. Therapy and medication for associated symptoms are by far the most common treatments, though do not completely resolve issues and the unique needs of each immortal affected by the condition need to be taken into account on and individual basis, as no two treatments are the same, nor will every immortal have the same or all symptoms. For memory loss in particular, it's recommended that immortals keep journals and records of their life to prevent some distress at bay when dealing with memory loss. Most immortals also attest to that keeping at least part of their social circle filled with other immortals who were not born such also is a major factor in dealing with their symptoms, as having close bonds with others like themselves can keep symptoms at bay and they are better able to trade tips to deal with their situations. Having friends and loved ones who face similar ordeals also is stated by many to greatly alleviate feelings of isolation. Forming long term goals, even if solely out of spite, is also a common tactic among immortals for dealing with immortality fatigue. It is thought that by giving themselves goals, often those that may take centuries or are outright impossible, to work to give a sense of purpose that can keep depression and suicidal thoughts at bay. Many immortals attest to that spite is an incredible driving factor, such as giving themselves a goal of outliving certain individuals or even entire nations can be enough drive to find purpose, often finding other smaller and more achievable goals in the meantime.
As there is no one definitive cause to immortality fatigue, there is also no one agreed upon prevention. It is thought that most immortals and omnia who had become such, rather than born it, will suffer at least for a portion of their lives that is attrivuted to the condition.