Perhaps he has a sickness or illness in the context of the fanfiction. It could be a magical malady that affects his stomach and makes him vomit.
Maybe he ate something bad in the fanfiction world. Like some enchanted food that didn't agree with him.
Perhaps he has been exposed to some sort of deadly and unknown substance in the mythical world. This could be a new type of monster venom or a strange plant that he accidentally ingested. The substance could be attacking his body from the inside, causing his internal organs to bleed, and thus he throws up blood.
Well, it could be due to some sort of magical potion gone wrong. Maybe he drank something that was supposed to give him extra strength but instead made his stomach turn. Another reason could be that he got poisoned during a battle with a monster. Some monsters might have venom or toxins that could make him sick to his stomach.
One possible reason could be that he was poisoned. Maybe he ate something given to him by an enemy who wanted to incapacitate him. In the Star Wars universe, there are many strange substances that could cause such a reaction.
Maybe he ate something that didn't agree with him. In the wizarding world, there are all kinds of strange magical foods. If he accidentally ate a spoiled or enchanted food item, it could make him throw up. For example, some magical candies might have unexpected side effects if not prepared correctly.
One possible reason could be food poisoning. If a teacher ate something bad before coming to school, it might make them throw up. For example, if they had some expired dairy products for breakfast.
Perhaps he has lost someone very dear to him. In the wizarding world, death is a constant threat. If a close friend or family member has passed away, especially in a violent or unexpected way, it could cause him to have such an extreme reaction. Losing someone can shatter a person's emotional stability, and for Draco, who has a complex personality, it might manifest as throwing up and crying.
There could be various reasons. For instance, motion sickness if a student has to travel a long distance on a school bus with a bumpy ride. Also, if a student has a pre - existing medical condition like migraines, it can sometimes cause vomiting. In addition, the smell in the school, such as from a science experiment gone wrong or a musty old classroom, might trigger the gag reflex in some students and lead to throwing up.
It could be related to a new and strange power he's trying to control. Percy is constantly evolving and getting new powers. If he tries to tap into a power that his body isn't ready for, it might have some adverse physical effects like vomiting. Like when he first started to understand his water - based powers, there could be something similar but more extreme with a new power.
One reason could be a stomach bug. Maybe you ate something bad before school, like spoiled food or food that didn't agree with you. Another reason might be motion sickness if you had a bumpy bus ride to school. Also, high stress or anxiety can sometimes make people feel nauseous and throw up.
One reason could be a hidden disease or affliction that is unique to the fanfiction world he is in. It could be something that has been passed down in his family magically. Or perhaps he has been in a situation where he was exposed to a harmful magical energy source for too long. This continuous exposure could gradually damage his body and result in coughing up blood. For instance, if he was trapped near a leaking magical artifact that emits harmful rays.