In a 'James Potter vomiting fanfiction' plot, there are several potential reasons. He could be suffering from a magical illness. Wizards can get sick just like Muggles, and some magical diseases might have vomiting as a symptom. He might also have overexerted himself magically. If he used too much magic in a short period, it could take a toll on his body and lead to nausea and vomiting. Another possibility is that he was in a situation where he was extremely frightened. Fear can cause the body to have a physical reaction, and vomiting could be one of them.
Well, perhaps he ate something bad. In the wizarding world, there could be all sorts of strange magical foods that might not agree with his stomach. Maybe he had a bad reaction to some experimental potion he drank. Or, if he was in a battle, he could have been affected by a dark spell that not only injured him but also made him vomit as a side - effect. Also, if he was under a lot of stress, it could cause his body to react in such a way. For example, if he was worried about the safety of his friends or family during a dangerous time.
One possible reason could be that he was poisoned. In the wizarding world, there are many dark spells and potions that could cause such a reaction. Another reason might be extreme motion sickness if he was on a wild magical ride, like on a particularly unruly broomstick or a flying magical creature.
The threat to his friends. James is very loyal to his friends, like Sirius, Remus, and Peter. If they were in danger or if something bad happened to them, it would be understandable for him to cry. For example, if one of them got seriously injured or was in a life - threatening situation, his emotions would be on full display.
One reason could be jealousy. Maybe Albus has some special ability or is getting more attention from their parents. Another could be that James is just following in the footsteps of the old school bullies he might have known, thinking it's normal behavior. Or perhaps he sees Albus as too different from what he expects a Potter to be.
One possible reason could be a dark magic influence on James Potter in the fanfiction. Maybe he's been cursed or possessed, causing him to act out of character and disown Harry.
It could be an exploration of the darker side of human nature. Writers may use these characters to show how relationships can go horribly wrong, even if it's not in line with the original story.
One reason could be for the sake of novelty. Fanfic writers like to create unique and unexpected scenarios, and this is a very different take on the Potter family. It grabs readers' attention.
Some fans might create it as a form of shock value. They want to stand out by presenting a very different and controversial take on the relationship between James Potter and Harry.
It could be a prank gone wrong. Maybe Loki or another mischievous character played a trick on Thor that involved some sort of potion or spell that made him vomit. This would add an element of humor and sibling rivalry to the fanfic.
Perhaps James had some hidden magical ability that he was unaware of until that moment. It could be something that was passed down through his family but had never manifested before. This ability could have protected him from Voldemort's killing curse. Or, it's possible that there was a plot by some other characters to save James. There could have been a group of wizards or witches who had been secretly working to keep James alive because they knew his importance in the fight against Voldemort. They might have used some sort of time - turning magic or a protective charm that Voldemort couldn't break through.
Perhaps Snape believes that James has some crucial information that he needs and he thinks torture is the quickest way to get it. Or maybe there's a power struggle going on. Snape wants to assert his dominance over James, who might be seen as a rival in some way, either for a position at Hogwarts or in the wizarding community. Also, it could be due to a misunderstanding that has spiraled out of control, leading Snape to think that James is a greater threat than he actually is.
In some fanfictions, it could be related to Lily. If James did something that Snape perceived as a threat to his relationship with Lily, even if it was just being overly affectionate with her in front of Snape, Snape might lash out at James. Snape had deep feelings for Lily, and any sign of James getting in the way could trigger an attack.