My first thought was that a shark had taken my right leg. I knew I was in danger. I expected to see my blood billowing around

I moved to Sydney, Australia, after finishing my master’s degree at Nottingham University. I was winging it: I just turned up with a suitcase. I got a couple of jobs, in internet marketing and as a private tutor, and met an Australian woman, Chloe. About a year after I arrived, I was off work on a beautiful summer’s day and fancied some peace and quiet, away from all the tourists who flock to Bondi. Chloe had told me about Gordons Bay, a small, secluded beach nearby, and I was looking forward to listening to music, reading and relaxing.

There was hardly anybody there and I settled on some large rocks to sunbathe. It was postcard perfect: serene, azure sky and a calm, green sea. It was the hottest part of the day and, after reading for a while, I decided to cool off and jumped into the water. It was warm and I remember feeling happy. I swam away from the rocks and kicked back to float, looking at the sky. That’s when the pain struck.

My first thought was that a shark had taken my right leg. I didn’t know what was happening, but I knew I was in danger. I expected to see my blood billowing around me in the water, but there was nothing. This magnified my panic; I didn’t know what was causing the pain or which direction to swim to avoid it.

My heart was racing and every one of my muscles tensed, then went into spasm. I was in blinding pain all over. I lost the ability to speak or think. My internal voice had stopped. I could barely breathe. I believed I was going to die.

I tried to swim, but felt very tired. I thought that if I went to sleep, it would all be easier when I woke up. But I went into autopilot and somehow managed to get myself to the rocks. There were thin red lines across my right shin that looked as if they’d been drawn with a pen.

A scuba diver ran over. He said he’d seen box jellyfish in the area. I wouldn’t have been able to see them in the water. I didn’t know then that they are one of the deadliest creatures on Earth. Their tentacles pump venom into the skin that attacks blood cells and can lead to cardiac arrest. He told me I’d been stung by one and needed to get to hospital immediately.

All my conscious decision-making facilities had left me, and I wasn’t able to process what he said. I walked away. He called after me, but my only instinct was to get home. The next thing I knew, I was in my apartment with a bag of peas on my leg.

I still don’t understand the sequence of events. I lay down, and for an eternity I didn’t move. I didn’t feel like I’d been awake or asleep. I couldn’t think of what to do or how to communicate. I was a prisoner in my own body.

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After a day or two, the poison began subsiding. My foot had swollen massively – my little toe was the size of a big toe. Those thin red lines had started corroding, and the poison had eaten away at my skin, revealing the muscle and bone underneath. It looked as if someone had taken a jagged axe and tried to chop off my foot. I managed to call Chloe and show her. The next thing I knew, we were on our way to hospital.

The doctor asked why I hadn’t come in sooner. I tried to explain. I asked if there was anything he could do, but he said the toxins had gone through my system: there was nothing they could do except clean the wound. He told me I was lucky the jellyfish had stung me on my leg; if it had been on my chest, I would not have made it.

I left Australia pretty quickly after that. I have a scar, still walk with a limp and have pain in my hip. I wonder about the long-term effect on my brain and body as a result of the toxins, but there’s very little data on this. I think my delay in getting treatment was down to the shock.

Chloe and I are still friends, although the relationship didn’t work out. I now run a startup in Silicon Valley. Sometimes I think about setting up a box jellyfish survivors’ group – Indigenous Australians say that you inhabit the power of any animal that stings you. That makes us pretty indestructible.

• As told to Sophie Haydock

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