In fanfiction, Naruto could feel sick due to overusing his chakra. He often pushes himself to the limit in battles and training, and this excessive chakra use might take a toll on his body, making him feel ill.
Another possibility is that he caught a strange disease while on a mission in an unknown land. Fanfiction often explores new and unique scenarios. He could have been exposed to some unknown pathogen that his body has no immunity against, leading to his sickness.
Maybe in the fanfiction, he was poisoned. There could be an enemy who managed to slip some kind of toxin into his food or drink. This poison could be slowly affecting his body, causing him to feel sick with symptoms like weakness, nausea, and dizziness.
Well, in the fanfiction, perhaps Naruto realizes that Konoha's politics are too complex. There are always hidden agendas and power plays. He, being a straightforward person, might get tired of all the behind - the - scenes stuff. Also, he may feel that his friends are changing because of Konoha's influence. For example, they might be more focused on the village's reputation rather than their true feelings, which makes Naruto sick of it all.
Maybe he's tired of the same old dynamics. In fanfiction, sometimes the relationships in Team 7 can be written in a very repetitive way. For example, Sasuke's brooding and Sakura's one - sided love for Sasuke can become overdone, making Naruto feel sick of it all. Also, if the fanfiction focuses too much on the team's conflicts without any real development, it could be a reason.
Maybe Naruto is sick of Sakura in fanfiction because her character is often portrayed as too pushy or one - dimensional. In some fanfictions, Sakura might be overly obsessed with Sasuke and Naruto just gets tired of her constantly going on about it.
One reason could be that the fanfiction often portrays the characters in a very different way from how he knows them. For example, if it changes their personalities too much, it might make Naruto feel like it's not the same team he belongs to. Another reason could be the overuse of certain plot devices in the fanfiction. Maybe every story he reads has the same cliché situations, like the team always getting into the same type of trouble in a very predictable way. Also, if the fanfiction focuses too much on relationships that Naruto doesn't see as important within the team, it could put him off.
Maybe Naruto has seen too many unrealistic or out - of - character portrayals of Konoha in the fanfiction. For example, some might make Konoha overly cruel or its people too stupid, which goes against his understanding and love for his village.
One possible reason could be that he has been through so much trauma that he has numbed himself. For example, all the losses he has endured during his battles and in his personal life might have made him build a wall around his emotions.
One reason could be that he was exposed to some kind of harmful chakra or energy in the village. Maybe some leftover dark jutsu residue affected his weak baby body.
In fanfiction, one possible reason could be that he was exposed to some kind of harmful chakra. Maybe an enemy sent a weak but insidious chakra wave towards him when he was just an infant, which gradually made him sick. Another reason might be related to the poor living conditions he was in. Since he was alone as an infant without proper care, he could have caught a disease easily from the dirty environment around him.
His parents' death also contributed to his loneliness. Growing up without them, he didn't have that family support and love that most kids had. He had to fend for himself and deal with his feelings of abandonment all alone. And in the fanfiction, perhaps his friends are too busy with their own missions or problems, leaving him feeling isolated.
One reason could be his status as a jinchuriki. People might be afraid of him because of the Nine - Tails inside him, so he feels unloved. Another reason is that he was an orphan, and without his parents around, he may have felt like he didn't have that family love that others had.