Anna Wardley, aged 40, had to abandon the swim between Menorca and Mallorca after being bombarded by hundreds of jellyfish stings.
Endurance athlete Anna was more than 11 hours into the challenge when she went into shock due to the stings, experienced convulsions and lost the use of her right arm.
She had to be rescued by her support team.
Anna, of Bradfield, who was swimming through the night, said: “If you want to create a picture of pure hell, I was there.
“It was like having hydrochloric acid thrown all over my body, layer after layer, as I got stings on top of stings on top of stings.
“I was completely exposed to the onslaught in just my swimsuit and was absolutely determined to keep going – I was throwing everything I could back at the jellyfish.
“I used every strategy I could to cope. I kept telling myself that I just needed to keep swimming, but in the end my body started to shut down.”
Anna was taken to hospital, where she was treated with steroids.
She said her passion has been fuelled by her fundraising efforts to support three Spanish charities – Marine Inspirations, Joves Navegants and the Marine Animal Rescue Project.
To find out more about Anna, visit: www.facebook.com/AnnaWardleyEnduranceSwimmer/