Here's just a little headcannon I came up with.

Percy Weasley was always described as studious, overly serious, and a stuck up. But what most didn't know is that there was a reason for this.

"Percy, slow down!"

"Come on!" Percy called. "Mum said to be back by sundown and it's nearly five."

The three young boys walked across the field and into the woods.

They explored the area, pointing out the various plants and animals, playing, and being children.

As the hour went past, Percy suggested that they play hide and go seek.

Percy said he would count first and covered his eyes in the crook of his elbow against a tree.

". . .3. . . 2. . . 1. . . Ready or not, here I come!" He shouted into the trees.

He found George pretty quickly, since the boy had forgotten that his bright red hair would stand out against the bush he was hiding behind.

The two looked around for Fred, but couldn't find him.

But soon, they could hear his cries, "PERCY! PERCY, HELP!"

Percy sprinted to the sound of his brother's voice. He came to the base of a tree when, "Up here!"

Percy looked up into the branches and saw Fred dangling from one about ten feet up.

He immediately started climbing the tree, not even waiting for George.

He eventually reached the branch above where Fred was and reached out his hand to him.

"Come on, Fred," he said. "I won't let you fall, I promise."

Fred moved his hand from the branch into Percy's palm and then Percy used his other hand to grab Fred under his other arm.

He pulled him up and set him onto the branch where he was dangling from and let the boy catch his breath.

"Are you okay?" Percy asked

Fred just nodded his head and looked down at his feet.

Percy made him look him in the eyes, "Hey, it's alright. You're just fine. Come on. Let's get down from here. "

Fred nodded and the two began to make their decent.

As Percy stepped onto the branch just below the one he was sitting on, he heard a loud crack, followed by Fred screaming, "Percy!"

There was a brief period of open air, before he was hit multiple times by the tree's branches as he fell. One branch hit his shoulder and pain laced through his arm. Percy screamed out in pain as he felt his leg break and pain shot up through his entire right side. When he finally reached the ground, he felt his head hit a rock and the world began to spin. 

He saw George run up to him, "Percy? Percy, are you okay? Percy, answer me!"

Percy couldn't answer. The pain was overpowering his senses, and he couldn't think straight. 

As the world began to spin even faster, colors blended together and his little brother's face turned into a blob of color and the sound of his calls faded away. 

Percy began to close his eyes and the world dissolved into darkness.

Fred scampered down the tree and saw Percy lying motionless on the ground, his glasses askew, and his limbs at odd angles. His leg was bent in a weird way and made Fred feel like being sick. 

George was shaking his shoulder, trying to get their older brother to wake up.

Fred knelt beside his brother and shook him, tears streaming down his face.

"Percy! Percy wake up! Please, Percy! I'm sorry, Percy. I'm sorry I climbed the tree."

George stood up and took off running, "I'm getting Mummy," he yelled over his shoulder and left Fred alone, hugging onto their brother's limp form. 

George ran faster than he had ever run before. Out of the woods and across the field and through the back door where his mother, one of his other brothers, Charlie, and his five-year-old sister, Ginny were sitting at the kitchen table.

"Georgie!" Ginny said. "Come color with me!"

George ran up to the table, "W-w-we were p-playing a-a-and Fred. . . The tree, and p-p-Percy a-a-and-"

"Slow down there, George," Charlie said. "Tell us what happened, slowly."

"We were playing hide and seek, a-and Fred hid in a tree, but something was wrong because  he was yelling for help, b-but Percy ran ahead of me. When I got there, Percy had fallen out of the tree or s-s-something, and he's just laying there."

George was in tears at that point and Charlie knelt down in from of him, putting a comforting hand on his shoulder.

"It's okay, George. Can you show me where Percy is?"

George nodded and Charlie took his hand as he led him into the woods.

Fred had given up on trying to wake up his brother and was just laying curled up at his side. He heard footsteps in the distance and stood up, looking around the trees.

"It's just around here, somewhere," he heard George say.

He saw his twin leading Charlie and his mother, who screamed when she saw her son in such a horrible position. 

"I'm sorry, Mummy," Fred choked out. "It was an accident, I swear."

"I know it was, Fred," she said, hugging him. "Now, you and George go back to the Burrow and wait for us there, okay?"

Fred wiped at his eyes, "Okay, mummy."

Percy woke up to people shuffling around and talking. He hurt all over, his head was pounding, his shoulder was on fire, and he couldn't even move his leg.

He opened his eyes and was looking up through the trees at the light fading from the sky. He tried to sit up, but instantly let out a whimper as pain shot up through his entire body. 

"Lay down, Percy," his mother's voice said. "It's going to be okay."

Percy let his head rest back down, but remembered how he had fallen in the first place. 

"Is Fred okay?" He asked. "He didn't fall, too, did he?"

"Fred's just fine. A little shook up, but he's fine."

He tried to turn his head but felt that he couldn't due to something keeping his neck from moving. A fresh wave of pain caused his body to shake.

"Mummy it hurts," He whimpered as tears began to fall. 

"I know, Percy," He could hear her crying and her voice cracked. "These nice wizards are taking you to St. Mungo's and they'll help you, okay?"

"Don't cry, Mum," Percy told her. Percy hated it when his mother cried. 

"Oh, don't worry about me, dear."

He suddenly felt himself being lifted up into the air, "Mummy!"

"Shh, don't worry, Percy. You're safe."

He then realized that he was being lifted up on a stretcher and they were carrying him out of the forest.

"Mummy?"

"I'm right here, Percy," He felt his mother gently take his hand and rub her thumb over the back of his hand. 

Percy suddenly began to feel very tired, "I think I'm going to go back to sleep, Mum."

"That's okay, sweetheart. Go right on ahead."

As Molly Weasley watched Percy's eyes close, she finally let all the tears fall. Of course in a house with seven children, they were bound to get hurt, but they were never so sever that they needed to go to St. Mungo's .

As the healers loaded her son into a muggle vehicle she asked, "Wouldn't it be quicker to apparate?"

"Not with him in this state. Apparating with someone injured, especially this age, it would only make it worse."

Molly hugged Charlie to her. The fourteen-year-old tried to soothe his mother's tears, but eventually just let her cry. He knew how hard it was for her to see Percy that way. 

It was hard for him, too. His stomach was in knots every time he looked at the bruises and cuts that covered Percy's body. He wanted to cry when they put on the brace to keep his neck in place as to "not make the damage worse". When they had to pop his dislocated shoulder back in place, he was so scared that Percy would wake up right then.

He just wanted to run around and play with his brother when they cast a spell that created a cast of sorts that went all the way up Percy's leg. He wanted to run and hide when they told his mother that they were lucky that he was even alive.

Charlie just wanted to go back and time and prevent it from ever happening

Arthur Weasley left the Ministry a soon as he read the note at his desk.

Percy's hurt-come to St. Mungo's

It was Bill's handwriting, but that didn't matter. All that mattered to him was getting to his son. He apparated to the hospital and was directed to the correct floor. 

He opened the door and saw Percy lying motionless in the bed, his wife running her fingers through his hair, and Charlie sitting in a chair off to the side.

He hurried to Percy's side and looked at how still he was, "What happened?"

"He and the twins were playing hide and seek and Fred hid in a tree. I think he slipped and was hanging from one of the branches and Percy had to climb up and help him, but the branch Percy was on broke," Molly said. 

"Is Fred alright?" He asked.

Molly nodded, "He's just a little spooked."

Arthur ran his thumb across a bruise on Percy's cheek, "Will he be okay?"

"The healers said that he hit his head pretty hard, dislocated his shoulder, and broke his leg, but they were able to fix that really quick. They're keeping him until tomorrow afternoon, but he'll be back to normal in a few days. They said that we were lucky."

"Lucky? How could they consider all that lucky?"

"They said-they said that if he had been a little higher up, or fallen in a different way, he would have broken his neck and been paralyzed forever or it-it could have even killed him."

Arthur stared at Percy. It felt so unnatural to see the boy so still. He just wasn't a still child, he always wanted to be moving, playing, and having fun. Even when he was asleep he was restless. 

But right now there was no emotion on his face; he was just there. Arthur suspected that he wouldn't look much different if he were dead.

The next day, when Percy walked into the Burrow, Fred just about barreled him over in a hug, "I'm sorry, Percy. I really am."

"I know, Fred."

After that day, Percy only read or studied. He never played, he never misbehaved, he never acted like a kid. 

Fred and George tried to get him to play with them, but he just went to his room and locked the door. They made it their life's mission to make him smile again.

Everyone just assumed that he was scared for his own well being, that the accident had scared him and he never wanted something like that to happen again. That he knew he could have died.

But the truth was, whenever he thought about that day, the only thought that crossed his mind was, "What if it were Fred?"