I don't know how to feel. Part of me is relieved that I made it back alive, but I feel guilty that my relatives and my people are dying. I have only minor physical injuries, but the mental scars are still there. I don't sleep well at night and I often wake up screaming. Most people in Syria don't have the option of running away like I did. But I am glad to be alive.

My parents came to the UK from Syria in the 1970s. My dad is a doctor and my mum is a teacher. They're both Sunni Muslims. They'd been living here for the best part of 20 years when I was born in 1993 and always kept in touch with their family at home. I grew up in Britain, but spent many school holidays with relatives in Damascus.

Neither my parents nor my family in Syria ever spoke much about politics because they were scared about the repercussions. My parents grew up in Damascus under the Ba'athist regime where it was dangerous to speak your mind. Even in London, they were afraid that if they spoke out of turn it would cause problems for their relatives – their friends would sometimes talk about the Syrian embassy in London keeping tabs on British Syrians who were too openly political, intimidating their families back home. I never knew whether these stories were true but I didn't have much reason to challenge them.

When the revolution started in 2011, I was excited at the thought of change. It seemed far away from my own life in London, where I was finishing my A-levels. Then my 24-year-old cousin Zafar disappeared. He had been walking past a protest and was arrested and imprisoned. It was impossible to find out where he was. We panicked. When I spoke to his dad, my Uncle Ali, he said all the young men he knew had been detained at some point and that "Inshallah, he will be OK". Zafar was released a few weeks later. Everyone said he was different afterwards.

As the months went on, things got really bad. Our Syrian friends in the UK were anxious about their families but people weren't talking much about the war. My mum's family live in central Damascus, which has stayed relatively safe, but my dad's family are in a south-eastern area of the city that was a government target because there were a lot of rebels there. In September last year Uncle Ali, Dad's brother, was killed. I had always been close to him. Zafar told me that it was impossible to relocate to a safer part of the city because of military checkpoints. The family was stuck there. Over the months, I heard my cousins get angrier. Zafar and his brother Mohammed – who is 25 and only four years older than me – joined the rebels, the Free Syrian Army. They weren't the kind of guys you would ever imagine to be fighters but they didn't feel they had an option.

After my uncle had died, I lost interest in college, where I was studying graphic design. It felt irrelevant and I wanted to go to Syria. My cousins warned me to be careful but said they would look after me if I went. My parents tried to stop me but my mind was made up. Because of sanctions, it is impossible to fly directly to Syria from the EU, and fighting near the airport makes it difficult anyway. In April this year, I booked a flight to Beirut.

My cousins helped me arrange the overland journey from Lebanon. It was terrifying; nothing prepared me for what I saw when I arrived. My uncle's house was still standing but the streets around it were unrecognisable after months of shelling. My cousins were different too. Before the war, Mohammed was training to be an engineer. He was always pretty nerdy but now he was authoritative. He told me his mother and sisters had managed to get to south-western Damascus. It may sound like a small difference, but the area they had fled to was not under rebel control, so it was much safer. They hadn't been able to get residents' permits so were living in hiding. If the soldiers realised where they came from, they might have suspected them of rebel involvement.

I don't know what I expected to see in Syria and it's hard for me to talk about it. I think a part of me thought my British passport (I'm a dual national) would protect me, or that my presence there would make a difference. That was naive and wrong. It was impossible for me to be useful. I'd never done national service or any military training and I didn't know how to handle a gun. After growing up in London I wasn't even comfortable being around guns, which I had to get over quickly. My cousins didn't want me to get killed and I spent most of my time at the base camp, which was in a building that used to be a school.

A Free Syrian Army fighter in Damascus. Photograph: Goran Tomasevic/Reuters

On my journey from Beirut, I'd passed through some parts of Damascus that were still functioning: shops were open, schools were running and people were out on the streets. But this area had practically shut down. I spent time sorting out meals and supplies of food and water for our group, and helping the injured. There were long stretches of the day where there wasn't much to do except watch the camp with a couple of others. Some of the other rebels were boys I'd known as a kid. Some made fun of my English accent in Arabic. Sometimes my cousins were impatient with me. I could understand why.

Soon after I arrived, Mohammed taught me to use a gun so I could protect myself and the camp if I needed to. At first it was exhilarating to fire the gun and I was frustrated that my cousins wouldn't let me go out with them to fight. A couple of times I drove out with them to the frontline. Some of these trips were uneventful, but the second time there was gunfire and explosions and one of our battalion died right in front of me. I realised that even though I had learned to handle a gun, there was only so much it could do to protect me.

I saw and heard things that I will never forget. I was kept awake at night by the sound of bombs and the screams of people dying. I saw people with their limbs blown off, and worse. I remember one particular bomb attack that killed a lot of people. There was a makeshift hospital in a building that used to be a grocery shop. I tried to help. It was like being in a nightmare. I wasn't injured but I was covered in other people's blood. One woman had lost four children and she could not stop screaming. I can't forget the expression on her face. After two months, I spoke to my parents and I started crying and I couldn't stop. I decided to go home.

It wasn't as simple as just jumping on a flight back. There were a lot of checkpoints and soldiers around and travelling by road was a risk. The scariest thing about being in the middle of a conflict is that no laws apply. It sounds obvious, but realising that there is no one and nowhere to run to if something bad happens is deeply shocking. There was a period of a few weeks where I was waiting to leave, and I felt as if everyone was angry with me. Eventually, someone agreed to take me in their car and I got to central Damascus, where I found my mum's family. When my aunt saw me, she started to cry, and then she slapped me and told me I was stupid. I didn't stay there for long. I was paranoid that the army would realise I'd been with the rebels and target these relatives. I booked a flight home from Beirut and my aunt managed to find a taxi driver who would take me across the border.

After I got back there were chemical attacks in Damascus. In September – a year after his father was killed – Mohammed died in an air strike near where our base had been. I thought it should have been me. I failed. It's hard to talk about him. He was one of the bravest people I will ever know.

Some names have been changed