Last September, I made a split-second decision that changed my life.

At 10.30 in the morning, I was on the bus going to my studio in east London when three teenagers got on and started mucking around, upsetting the other passengers.

At 6ft 6in I'm not easily intimidated, so I decided to step in, hoping to calm them down. It wasn't bravery; I just couldn't live with myself if anything had happened while I stood by. One of the youths had his legs blocking the aisle and was swearing at anyone who wanted to get by, so I leaned over and said, "Excuse me, but you need to mind your language and behave yourself."

I thought my comment was pretty reasonable, and wasn't said aggressively, but it was like unleashing a caged animal. He came raging over to me, literally frothing at the mouth and started screaming in my face, asking who I was to question him. I knew that if I stood up, my height would inflame the situation, so I stayed where I was and calmly repeated that he shouldn't talk to people like that. He started spitting at me and gesturing at something in his pocket, threatening me with it. "I'm going to mess you up," he taunted.

I reminded him he was threatening me in front of witnesses, and he then said the scariest words to me: "I don't care, I will gladly mess you up and on camera too." He was frightening but I stayed calm and asked him to sit down and get on with his day, gently shaking my head as I did so. He reacted by punching me seven or eight times in the head, causing it to smash against the window. I blacked out for a couple of seconds but managed to stand up and pin his arms down. One of his friends came over and starting punching me in the ribs. Then he reached into his pocket and pulled out a knife. He stabbed me in the stomach – it didn't hurt, probably due to the adrenaline, but I knew immediately what had happened. "Stop," I said. "This stops now," and tried to back away. He stabbed me again, this time in the thigh, then him and his friends, one male, one female, prised the bus doors open and ran off.

I was bleeding profusely and was taken to A&E, where I passed out again through blood loss. As the room went white, then black, I remember thinking: "Is this it? Am I dead?"

I spent five days in hospital recovering from the knife wounds, concussion and a fractured jaw. The wound in my thigh had punctured my hamstring, leaving me bed-bound for seven weeks. As my body slowly recovered, my mind was tortured by the events on the bus. What could I have done differently? I tried to get my head around the actions of the young man too. How could he get to such a point where he felt able to attack another human being? Who had let him down? I spent hours imagining his childhood, trying to understand why he could do that.

I also felt desperately vulnerable – I was no longer in my happy-go-lucky bubble. For a while I didn't feel safe on the streets. I didn't want to go home to Melbourne, Australia, though – it wasn't London I was afraid of, but how your world can collapse so quickly and easily.

I was severely traumatised. My relationship broke down, and my career as an artist and designer ground to a halt as work lost its meaning. My life had been derailed by an event lasting all of two minutes.

The attackers were caught after seven weeks – a relief as it troubled me to think they could stab someone and be running around free to do it again. The young man who stabbed me was sentenced to 12 years and ordered to serve a minimum of six and a half.

Although I'm glad that justice was done, it wasn't a time for celebration. I feel incredibly sad that this young man's life has been thrown away. I wish him no harm.

After six months of thinking about nothing but the attack, I decided that something positive must come out of this, otherwise I would just fall into a black hole. I wanted to use my creativity to turn things around for people like that, so have organised Cut-It-Out, a creative, community-based project to support disadvantaged young adults.

If I was in the same situation again, I wouldn't hesitate to step in – I have actually told someone to stop hitting their child since. I've also been on that same bus again, but it wasn't a great experience; I don't like to be reminded of that day. I prefer to cycle to work these days.

• As told to Emily Cunningham

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