I'm not entirely sure what 'harry potter throw up fanfic' specifically means. It could potentially be a very strange or poorly written fanfiction related to Harry Potter that makes you feel 'queasy' in a sense, like it's so bad it makes you want to 'throw up'. But it might also be some sort of really out - there creative interpretation that involves a situation in the Harry Potter world where a character throws up or something really odd like that.
There was this time when my dad had the baby in his arms during a family gathering. The baby must have eaten too much because he threw up all over dad's shoulder. Dad didn't miss a beat. He turned to us and said, 'Well, looks like the baby doesn't like my cologne.' He then calmly took the baby to get cleaned up, all while making everyone around laugh with his easy - going attitude.
My dad was trying to feed the baby. But the baby clearly wasn't having it and threw up right into the bowl of food. Dad looked at the mess and chuckled, saying 'I guess that's one way to say no more food'. He then wiped the baby's face and started over with a new bowl of food, much more carefully this time.
Stress is a big factor. Just like the boy who threw up on his test paper. School can be really stressful with exams, presentations, and peer pressure. Some people's bodies react to this stress by making them feel sick to their stomachs and ultimately throwing up.
It's unlikely but not impossible. Usually, dogs don't respond to fictional fear in such a direct way. However, if the dog is highly stressed or has underlying health issues, intense fictional fear could potentially trigger vomiting.
A common reason is that he's under extreme stress. In the world of Hogwarts, Snape has to constantly balance his double - agent life. The stress of hiding his true allegiances from Voldemort and the Order of the Phoenix can take a toll on his body. So, it's not unthinkable that this stress could make him physically ill, leading to vomiting. Another reason could be his love for Lily. In some fanfictions, memories of her, especially painful ones like her death, can be so overwhelming that it causes a physical reaction like throwing up.
I don't have the exact name of the person who created the Omori manga at hand. It could be worth doing a search on manga databases or asking fellow manga enthusiasts for the answer.