A man who suffered constant pain after surgery cured it by taking a plunge in cold open water.
The man's case has been reviewed by doctors who suggest a short, sharp cold water swim may offer an alternative to strong painkillers and physiotherapy.
The 28-year-old man who suffered from post-operative pain found it disappeared totally after doing an open water swim.
However cold water swimming does not suit everyone and entails risks.
The man had been a keen triathlete prior to his operation and had found conventional treatments had made little difference to his severe pain.
His story is detailed in the journal BMJ Case Reports.
Report author Dr Tom Mole, from the University of Cambridge, said he hopes that it "gives new hope to people recovering from pain after surgery".
The man, who suffered from excessive facial flushing, underwent an operation (endoscopic thoracic sympathectomy) that cut the triggering nerves inside his chest.
The surgery went well but afterwards he suffered from severe, persistent pain which caused him a "great deal of distress".
He found conventional treatments had made little difference to his severe pain. He said exercise and movement in his physiotherapy sessions made the pain worse, which prevented him from completing his rehabilitation.
A keen triathlete before his operation, he decided to do an open water swim to take his mind off the pain.
The man, who has not been named, said it was a "long shot" as to whether it would help his pain but he was "desperate to get some relief".
The swim entailed plunging into the water from a rocky outcrop and swimming for around a minute before he could reach somewhere to safely climb back ashore.
"I initially thought 'damn this is so cold I'm going to die!' and I just swam for my life," he told the report's authors.
"Once I was in the water, I had tunnel vision - for the first time in months, I completely forgot about the pain or the fear of shooting pains in my chest if I moved.
"My entire body tingled with the cold. I just knew if I didn't keep swimming, I'd soon freeze. After a few moments I actually enjoyed it - it was just an immersive rush of adrenaline.
"When I came out of the water, I realised the neuropathic pain had gone away. I couldn't believe it."
The authors believe it is the first case of its kind documented, although cold water baths have been used in sports medicine to ease injuries.
Although it is unclear why it apparently cured his pain, they say there are some possible explanations:
The authors caution it is only one patient and say more research is needed "to assess the replicability and feasibility of forced cold water swimming as a potentially effective, natural intervention to enhance recovery outcomes from common post-operative complications".
The authors warn that cold water swimming is not for everyone - and there is a significant risk of hypothermia.
There is also a risk from the body's acute cold shock response, which may affect the arm muscles while swimming and can lead to incapacitation and potential drowning within minutes if unsupervised.