Disclaimer: I do not own Harry Potter, or else I wouldn't be writing here.
Here's the next chapter. Hope this gives you all the background you need and fills all the gaps, if not, let me now :D BTW, if any of you wondered how he knew she was possessed, it's because he has a sixth sense XD
For the next couple of weeks, Harry spent every waking hour researching about that suspicious hospital and about possessions. He went to the library every single day, and his friends were starting to worry. Since Ginny was attacked, they had all changed their minds about Hermione. They all thought now she was asolutely crazy and they were thankful she was taken away, they didn't want to be next on her list. They thought he was becoming obsessed, and they were right, but they couldn't understand the situation from his point of view, thay weren't there like he was.
The ginger girl had spread the word about that night, and she had portrayed his best friend as a mad woman with killer incstincts who would take out anyone who stepped on her way. The story had become so popular, it even made it to the newspapers. Everyone was talking about the girl-who-lost-her-way-and-became-a-murderer-in-the-eyes-of-all-even-though-she-hadn' rumours made her look worse than the deatheaters. The articles proposed she was insane, and was probably plotting the world's conquest through sick methods of torture, and if she wasn't kept under control, she could become the next person to bring darkness to the magical world.
Harry thought they were all making stupid predictions, but he could understand that they were scared. The world was just recovering from a war against the darkness, and he had to admit, that one of the most important faces that fought for the light had suddenly lost her mind was very discouraging. If she, one of the bravest and truest persons had tried to kill someone, who was safe anymore?
Meanwhile, from his research he found out many interesting discoveries. About the hospital St. Heathsburg, he learned it was an institution meant especially for mental issues since 1784. Magical families had had members with different mental problems since always, like muggles, but these persons were a disgrace for the families, so since the eighteenth century, several institutions appeared specialized in the care of the mentally injured. Pureblood families saw this as an oppurtunity to get rid of what they were ashamed of, so they sent them to this places. St. Heathsburg became the most popular because they also accepted those people who didn't have any kind of trouble, but their families thought to be a burden, so they give them mental problems. St. Heathsburg was only meant for purebloods, but since halfbloods and muggleborns became important members of the magical community and the pureblood mania was losing it's strenght -also because of the wars- they opened their doors to everyone. However, the magical community wasn't nearly as advanced as the muggle community in that matter, not that they were really making an improvement. They were still using electric treatments and experimental drugs to fight against the illnesses. Their methods were old and didn't work, so he was really worried thay would hurt Hermione and make her condition even worse.
About the possessions aspect, he had to sneak into the restriction section. Yes, he had to sneak, even though he had saved them all, he still wasn't allowed to go in there. Anyway, what he found wasn't very pretty. Possessions ocurred when a spirit took control of a living person's body. There were many ways to possess a person, involving many dark rituals. The spirits that possessed people most often were dead people who didn't want to leave the living's world, but they weren't ghosts. They wanted to be alive again, they refused to die, so they looked for bodies to occupy. They couldn't control things like normal people, but they could change the surroundings and the energy. The process took time. What they usually did to possess somebody was suck their energy to weaken them and being able to break through their natural barriers. Once their barriers were low enough, they could get inside of them and start controling them. The more energy they sucked, the easier it was to possess them. That's why the most common symptoms of being possessed was visible exhaustion. Also, the person could show lack of desire to do anything.
If the spirit wanted to take full control of the body, they had to do something much darker. Unfortunately, he couldn't find out anything about full possession, because none of the books dug deeper into that aspect. It was too dark, so the authors didn't want the readers to learn about it. He was reminded of the time he was researching about horrocruxes, the same thing had happened. He couldn't understand why people with knowledge prefered to keep it hidden, maybe because they thought it was dangerous. But, the truth was, it was far more dangerous the lack of information. He had experienced it personally.
Anyway, his deep research had given him answers, but it had also given him more worries. Now, there was no doubt he had to see her urgently.