I thought she was out for a swim in a wetsuit, but as we got nearer we saw she was fully dressed, lying on her back in the water

My husband Chris and I had been on Brighton beach for only half an hour and it was deserted. A week of sunshine at the end of August this year had abruptly ended and it had been pelting down all day. Miraculously, just as we’d reached the dog-friendly part of the beach, it had stopped raining.

Rosie had been haring about the beach, tail up, while Chris and I walked along the seafront. “This half hour has made this trip worth it,” I said. We’d almost cancelled our plans to go to Brighton for the day as the weather had been so foul.

When I first saw her, I thought she was out for a swim in a wetsuit. But as we got nearer, we saw she was fully dressed, lying on her back gently sculling the water with her hands. We hesitated: we knew this scene wasn’t right.

Then we heard her: “Help, please, I don’t want to die.”

We ran to the shoreline. I shouted over: “We are here, you are not going to die, we won’t let that happen. Can you swim to us?”

It quickly became apparent from her distress that she had gone out there with the intention of drowning herself, but had then changed her mind.

I remember thinking, I can’t believe this is happening; that it is down to us to get this woman out of the water. I looked around to see if there were other people we could share the burden with, but we were alone.

We could see she was disoriented, exhausted. She kept swimming away from us and then would change her mind and try to come back inland. Chris was getting ready to jump in, but with no one else around, I panicked about how I’d get them off the beach without help. I tried one last time. Rather than being nice, I found myself getting bossy.

“You asked us for help, you want to live, now you must swim towards us,” I said. “Stop swimming away. Just focus on my green umbrella, swim to it and don’t stop.”

She seemed not to be moving, until suddenly she was within reach and I waded in to catch her hand. She slumped to the sand. I sat next to her and asked her name. She was my age and kept saying how sorry she was for wasting our time. I couldn’t imagine how much pain she must have been in to feel that desperate.

We needed the woman to get to her feet; she was so cold, we couldn’t keep sitting there with her soaked through. We were worried she was becoming hypothermic.

“Shall I let you into a secret?” I said. “Four years ago, almost to this very hour, I was taken down to an operating theatre to have a double lung transplant. My life was saved by a stranger, and now here we are, strangers helping you. Please don’t apologise, we are glad to be here.”

That was the reason Chris and I had taken the train to Brighton that day: to mark the anniversary of my transplant.

Before that operation, I was on oxygen, using a wheelchair, unable to wash by myself. It had taken everything I had to cling to the belief that a better life was waiting for me if I could hold on. The woman on the beach broke my heart when she said I’d deserved to get better, but that she didn’t. I told her we were both just very ill and needed to let other people help us sometimes.

Experience: writing help in the sand saved my life Read more

We got her changed into a spare windbreaker, and managed to get her to walk back to her friend’s house, who was distraught at her absence. The last I saw of her, she was sitting on a balcony, smoking a cigarette, wrapped in a blanket. She’d asked for one more minute before she talked to the paramedics we’d called for help.

The whole episode took 30 minutes, but the odd coincidence of it still makes it feel like a scene from an unfeasible movie in my mind. Every day, I think of the stranger who saved my life; I never contemplated that I would be able to save a stranger in return. That evening one of my friends texted me back to say: “Your donor was able to give yet another gift to this world.”

• In the UK, Samaritans can be contacted on 116 123. In the US, the National Suicide Prevention Lifeline is 1-800-273-8255. In Australia, the crisis support service Lifeline is 13 11 14. Other international suicide helplines can be found at www.befrienders.org.

Do you have an experience to share? Email experience@theguardian.com