“Explain how the time inconsistency of optimal monetary policy can lead to a stabilisation bias. How would the introduction of a price path target help to address it?”

After reading the question three times, I still couldn’t make sense of it. I groaned, went back to the textbook, tried to read, made a cup of tea, and tried again. Nothing improved my focus. Then my phone lit up with a message from my friend Anisa: a picture of my name spelled out in Scrabble letters.

On my way. Stay there, I replied.

Perhaps a little break was what I needed. It was only 10.30pm, early by my standards. And, maybe, if I asked nicely and she was in a good mood, Anisa would come back to my room and explain the essay question to me. I left the textbook on my desk and grabbed my coat.

Outside, the moon lit up rows of daffodils, and the fresh cut grass stuck to my shoes as I crossed the playing fields. At the farther-most edge of Lady Margaret Hall’s gardens sat my destination – an old potting shed that the college calls “the summerhouse” and students call “the shack”. It had three walls clad in clapboard siding, small rectangular windows, and a wood-shingled roof covered in moss. The builders had left the fourth wall open to nature. Sometimes I sat in the shack alone and listened to the rain splashing off the roof or watched otters play on the riverbank. It was one of my favourite places on campus, like something out of a storybook.

Inside was a wooden bench, chairs and two small tables. On one wall, shelves held broken plates, green and blue glass bottles, and a bowl of old keys – treasures dug up by the gardeners. On the opposite wall, three old mirrors hung above a bookshelf containing weather-beaten board games, pillar candles and the occasional book. Dozens of loose Scrabble letters were scattered around the shack; students used them to spell out their names, an impermanent version of writing “X was here” on a bathroom wall.

Anisa was sitting with two boys I recognised from the business course, around an unusual object on the table between them. The clear glass container had a smaller glass tube poking out at the base and looked like something nicked from the chemistry lab.

“Hi guys,” I said, nodding to the room. “What’s that?”

Without answering, one of the boys picked it up and hovered a lighter over the smaller tube. I heard a bubbling sound and he disappeared behind a cloud of smoke. The smell answered my question.

It wasn’t the first time I’d been around people smoking weed. I’d even tried it myself; my friends shouted confusing instructions like “You have to inhale! Swallow and then breathe out at the same time! No, breathe with your mouth, not your nose!” As far as I knew, I’d never been high, but it felt cool and grown-up to blow smoke in the air and lazily pass the joint to the next person.

“Your turn,” the boy said.

“Nah, I’ve done it before and it doesn’t work on me,” I replied.

“Chalk and cheese,” Anisa said. I gave her an exasperated look; she knew very well by now that I never understood her Britishisms. “What I mean is,” she continued, “a bong is totally different from a joint. Much more effective, fit for purpose.”

Fine, why not? I’m already out here, might as well have a new college experience. The boy to my right held the lighter while I lifted the bong to my face. Then my face filled with smoke, and I doubled over, coughing. Anisa laughed. Everyone took a turn while we chatted about our holiday travels.

Eventually it came back around to me. “OK, one more, but this is it,” I said. I held the lighter myself this time, brought the mouthpiece slowly up to my face, and didn’t cough. I sat back in my chair and zoned out while the others continued their conversation.

At some point, I looked at my phone and saw it was past 1am. How is that possible? I’ve only been here for a few minutes. My mind tried to fill in the gaps, to find a logical explanation for where all the time went, but everything was blank. How did I just erase two hours of my life without realising it?

“I have to go,” I said.

“I’ll walk with you,” Anisa offered.

The short path back to the dorms seemed to stretch out for miles. My legs felt heavy and rooted to the ground. What’s wrong with me? I thought. Walking required a conscious effort, and it seemed like another hour had passed before I managed a single, stumbling step. “Sorry,” I said to Anisa. “Just … feeling wobbly.”

Then the muscles around my legs started to twitch and then my knees locked up. I couldn’t move. Just take a step. One foot in front of the other. My brain was sending signals into a void. Again and again, no response, no movement. I balled up my fists, dug my nails into my palms, and tried again, more forcefully this time: Keep walking, Malala! When nothing happened, a cold, sharp fear climbed up from my stomach and settled in my shoulders. Then everything went black. As I started to pass out, the truth hit me: I knew this feeling, the terror of being trapped inside my body. This had happened before.

Suddenly I was 15 years old again, lying on my back under a white sheet; a tube running down my throat, eyes closed. For seven days, as doctors tended to my wounds, I was in a coma. From the outside, I looked to be in a deep sleep. But, inside, my mind was awake, and it played a slideshow of recent events:

My school bus.
A man with a gun.
Blood everywhere.
My body carried through a crowded street. Strangers hunched over me, yelling things I didn’t understand.
My father rushing toward the stretcher to take my hand.

As the images repeated in the same sequence over and over, I raged against them, trying to beat them away. This isn’t true! I told myself. The real Malala is the one trapped in this nightmare, not the girl on the stretcher. Just wake up and it will stop. Wake up!

I had tried to force my eyes open, to see something other than this carousel of horrors. Inside, I screamed; outside, my lips stayed closed, motionless. I was awake and buried alive in the coffin of my body.

And now, on a garden path in Oxford, it was happening again: my mind telling my body to move, my body turned to stone. “I can’t walk!” I finally cried out to Anisa. “Please help me!”

“Shhhh, I’m here, you’re OK,” Anisa answered, her voice strained with alarm. Strong from years of competitive sports, she lifted me up and carried me back to her dorm. I crumpled to the floor, exhausted and dizzy, struggling to catch my breath.

Everything was still for a moment. I felt relieved to be inside, in the comfort of my friend’s room. Then, out of nowhere, the images I had seen in the coma flashed before my eyes again: Bus. Man. Gun. Blood. It was like seeing it all for the first time, fresh waves of panic coursing through my body. There was no escape, no place to hide from my own mind.

“I need to go to a hospital,” I gasped.

Anisa sat down next to me. “You’re having a bad reaction, but this will be over soon – 30 minutes, an hour at most. If you go to a doctor, they might run tests. It stays in your blood.”

Seconds later I felt something caught in my throat, cutting off my air supply. I instantly remembered the pressure of the intubation tube, the sensation of choking every time I tried to swallow or speak. Gathering all my strength, I lunged into Anisa’s bathroom, leaned over the toilet, and vomited.

After a few minutes lying on the cold floor, I grabbed the sink and pulled myself up, catching sight of my pale, terrified face in the mirror. What is happening to me?

“Did that help?” Anisa asked. “Sit back down and let me get you some water.”

I took a deep breath and tried to calm down. It’s over, lean back, just relax. As soon as I closed my eyes, the slideshow began again. The images came faster now, relentlessly attacking me. My mind was freefalling deep inside my body. I opened my eyes and screamed.

“Malala, snap out of it!” Anisa yelled, shaking me by the shoulders. She ran down the hall and woke up a friend. They sat on either side of me, bracing my body upright. Anisa gave me a pillow to muffle the screams and wiped the sweat off my face with a damp washcloth.

We stayed on the floor for what seemed like hours, until the screaming and shaking had stopped. “Let’s get some sleep,” Anisa said. “You take the bed, I’ll pass out here. In the morning you’ll feel better, OK?”

I got in bed, but I didn’t sleep. I could still see a familiar world around me – her books on the desk, polo mallet in the corner, the waning moon shining through the window. If I closed my eyes, it would all be gone for ever. The nightmares would hold me hostage in an endless loop of terror. I drifted off only to jerk myself back to consciousness, jolting my body upright and slapping my own face. Wake up, Malala! If you fall asleep, you will die!

I was still awake in the morning when Anisa got up from the floor and stood over me. “I’m so relieved you’re OK now,” she said, tousling my hair. She stepped into the washroom and turned on the shower. I slipped out the door, hoping I wouldn’t run into anyone on the walk to my dorm.

Attempting to wrest control of my thoughts made me seasick. I sat at my desk all morning, trying to distract myself – social media, news sites, Candy Crush – but the replay of the previous night, the helplessness I felt collapsed on Anisa’s floor, kept creeping to the front of my mind and overwhelming me. I was nauseated, unable to stand up without feeling dizzy or sit down and be calm without shaking.

In the hospital, when I had finally come out of the coma, I had no memory of what had happened. Later I’d seen news footage of myself from the day of the shooting, bandaged and bleeding, carried through the street on a stretcher. In the video, the sun hits my face and my eyelashes flutter. Over the years, I’d seen that clip hundreds of times, but it never felt like part of my life. Those moments were a glitch in my timeline.

People always asked me what I remembered of the shooting. “My brain just erased it,” I told them. “One moment I was at school and the next I woke up in Birmingham.” I told myself that same story over and over – but now, I knew it wasn’t true. I had seen it all, and the memories were still lurking in my brain, years later. What had Anisa said?

It stays in your blood.
It stays in your blood.
It stays in your blood.

• This is an edited extract from Finding My Way by Malala Yousafzai, published by Weidenfeld & Nicolson on 21 October at £25. To order a copy for £22.50, go to guardian.bookshop.com