Sam Webster, 37, from England, suffered third degree burns and was left with horrific scarring when she fell from a banana boat while on holiday with her partner and young daughter.
Ms Webster told the Mail the stings felt like 'hundreds of razors' being sliced through her leg, leaving her close to drowning before her partner jumped in to save her.
Accompanying the Mail story are graphic photographs showing the burns.
She spent the rest of her trip in hospital and since returning to the UK has undergone two operations and faces further skin grafts to repair her leg, the Mail reported.
“I am scarred for life but just pleased to be alive and relieved that it wasn’t my daughter (aged six) that got stung. The pain was so bad I honestly thought I had been attacked by a shark.
"I’ve been through months of hell since this happened. I never realised a jellyfish sting could be so life-changing. I want to warn others,” the Mail quoted her as saying.
She says: "One minute I was laughing and splashing about, the next it felt like hundreds of razors were being sliced through my leg.
"I was screaming and panicking so much I started floundering in the water. I thought if I wasn’t eaten I would drown anyway, but luckily my partner saw and dived in to pull me back to shore."
Her calf was covered in huge red blisters and locals crowded round, some pouring cold drinks on her leg.
Ms Webster says: "I heard them saying it was a jellyfish sting but I was in shock. It felt like my leg had been dipped in acid."
A local policeman drove her to a nearby clinic in his pick up truck and she was treated with antibiotics and painkillers and taken back to her hotel to rest.
The next morning, Ms Webster tried to ignore the pain in her leg as the family had booked a rainforest excursion and her daughter was looking forward to feeding elephants.
But during the drive, her leg started to swell and the red blisters turned black. She was taken to a local hospital, but then transferred to a private hospital in Phuket.
It was there medics confirmed she had suffered third degree burns from a jellyfish sting.
"I was admitted for a week and they started clearing the spines out of my leg. It was agony."
Upon her release seven days later, Ms Webster, her partner and daughter flew back to England, where Ms Webster was admitted to hospital again.
Surgeons removed the top layer of skin and weeks later she had a second operation to remove the damaged tissue underneath, the Mail reported.
She spent the next three months recovering from the surgery on crutches and has only recently been able to return to work as a manager with the local council.
She told the Mail the trip was “meant to be the trip of a lifetime but it turned into a real nightmare”.
"I’ll never be able to wear shorts again and will need skin grafts in the future to help the scarring but knowing what I know now about jellyfish stings I was lucky. I could have died.
"I won’t ever be able to wear shorts or a bikini again. My leg is a mess.
"I want to warn others travelling in Thailand so it doesn’t happen to them. I honestly wish we had gone to Cornwall or Weymouth instead."