So, I started thinking the other day, what if it is all in Jacob's head. What if Jacob suffers from schizophrenia? At first I thought, come on, how much evidence could there possibly be? But I actually found a lot that matched.

Is Jacob a schizophrenic?

Schizophrenia check list:
1. Faulty perception: ✔️
2. Inappropriate actions or feelings:✔️
3. Withdrawal from reality and personal relationships:✔️
4. A sense of mental fragmentation:✔️
5. Speak in strange, confusing ways:✔️
6. Believe others are trying to harm them:✔️
7. Feel like they're constantly being watched:✔️
8. Social withdrawal:✔️
9. Depression:
10. Insomnia or sleep deprivation:✔️
11. Extreme reaction to criticism:✔️
12. Odd or irrational statements:✔️

Jacob is also possibly under all four types of delusions;
Delusion of reference, Believing an environmental event is believed to have a special or important meaning just for them
Abe's death

Delusions of persecution, believing something is about to get them
Hollows and wights

Delusions of grandeur, believing that they are a special person and that only they can do something
Jacob thinks he is the only one who can save peculiardom, and thinks he is special, a peculiar being.

Delusions of control, believes someone's thoughts or actions are being controlled by an outside force
Jacob can control the hollows

Jacob would also use neologisms, or made up words that only have meaning to him.

He has a lack of interest or enthusiasm. Jacob is always insisting he was ordinary, until the end when he realizes how extraordinary he is.

Jacob actually has a good chance of getting schizophrenia. It affects 1 in 100 people. It has genetic influence and environmental influence.

His grandfather may have also had it, which is why Jacob's father is often saying he needs to go to a home. And schizophrenia can also be found in children with early parental loss or separation. Jacob's parents both work so he probably didn't always see them when he was growing up.

Evidence: Jacobs parents are often asking Jacob if he is using drugs.
Jacob specifically said that his parents gave him pills and he didn't take them.
Ricky calls Jacob 'special Ed.' He claims he is a gifted student. Which he is. People with mental disabilities are often of higher intelligence than everyone else.
The stories Jacob's grandfather had been telling him turned out to be 'real.'
All the children have distinct personalities to be interpreted.
The last pages of Jacob's story involve him being locked away in a mental institution.
Jacob is constantly under pressure.

The real story:
Jacob's parents always knew their son had schizophrenia. But it never really got to a bad point until after his grandfather died. Jacob locked himself in his room and refused to come out. He never accepted his pills and became a social outcast. After some suggestions from Jacob's psychiatrist, he and his father went out to the island of Cairnholm, where Franklin Portman's grandfather had grown up. Jacob, rather than be healed, went into seclusion, this time spending long hours at the orphanage where his grandfather grew up. He enjoyed the darkness and quietness of the cairn on the island and slept there for parts of the day. Frank, becoming worried, enlisted the help of a few local fishermen to find his son. Jacob was up at the lighthouse, and shot at one of the men before running away. After a few weeks, Jacob thought the friends he had dreamed up needed to go to London. So he drugged his father and left. Franklin while in his haze, thought the children his son had mentioned in passing were in his room.
When Frank woke up, his son was nowhere to be found. He was frantic and didn't know where he was, so he called the American coast guard to search the beaches of the mainland.

Meanwhile, Jacob ran through forests and woods, still searching. He hitched a ride with a group of shady people traveling and made it eventually to London. He rode a train using money he had stolen from his dad and a few days later got hit by a car.

He was accepted into the hospital and admitted under John Doe. Meanwhile, his parents still searched for their son. The last they had heard was a phone call from their son, traced by authorities to be at a train station. Eventually they tracked down his hospital, but by then he had entered a comatose state. When he had awoken, he was taken back to the States.

But there was one problem. After he had been in the coma, his friends had all gone. His new psychiatrist started to talk to him, and he even seemed to be making progress. But then they found letters Jacob had stashed written by himself. At this point they were sad that their son wasn't going by any means to get better.
By then, a new drug had come out that let a patient go on thinking their thoughts without being bothered. They administered it in their driveway as they set out to the institution. This allowed Jacob to go on living his happy eternity for the rest of his life.

Who are all the characters:

Enoch represents all the kids that have ever bullied Jacob in his life. This is why Jacob's peculiarity is more important than Enoch's, and why Jacob always one-ups him. Jacob wishes his grandfather was still alive, and even though he eventually grew out of it, Jacob played around with action figures up until 7th grade, around Enoch's age.

Emma is Jacob's fantasy girlfriend. She has all the qualities Jacob likes in a girl. Smart, beautiful, fiery, and the ability to take care of herself.

Fiona and Hugh represent Jacob's parents. Fiona is nurturing and careful, she also loves gardening, but not having to work too hard to make the yard look nice. Jacob's father is more fun-loving and upbeat, usually doting on his wife and trying to become Jacob's friend. Franklin's always been nature oriented.

Horace represents Jacob's side that touches reality. Due to his illness, Jacob has trouble sleeping, and has been teased for how he dresses, because of his parents having more money. He also wants to know what's happening beforehand, so he can avoid being teased.

Claire and Olive are the sisters that Jacob always wanted but never got. When he was little, like some kids, Jacob bit people. He's never had a big fear of heights, either.

Millard is everything Jacob wants to be. Jacob wants to be recognized as a smart kid. He's had his share of objects he loves, and wants an equal he can talk to. Being invisible, Jacob doesn't have to worry about anyone making fun of his appearance.

Bronwyn and Victor have super strength so that absolutely no one can oppose him. Bronwyn and Victor always looked out for one another, and Jacob wished he had someone close to him to talk to.

In conclusion: There's lots of good points about Jacob being schizophrenic. No wonder his parents thought he was crazy! But when it all boils down to it, it's pretty obvious everything around Jacob is real. It just goes to show you, even in your ordinary life, extraordinary things can happen.