I'd got horrifically sunburnt while snorkelling at Kealakekua. But two days later when I was flying back to Chile, it was not so bad. I didn't even particularly notice it while I was on the helicopter flight over the volcano, though it was a little bit uncomfortable on the flight from Hilo to Honolulu.
I had two hours there before my flight to Houston, and I was just sitting in the departure lounge doing nothing in particular when suddenly I felt a sharp pain in my back. I sat up in surprise and felt another sharp pain. And within a few seconds, it suddenly felt like I was being stabbed repeatedly, all over my back.
I jumped up, unable to comprehend what was happening. It was excruciating and I could hardly breathe. I rushed to a bathroom and put some water on my back but it made no difference. I scratched furiously and it made no difference. I panicked and rushed around the airport trying not to shout in pain and that made no difference either. I was sure I would have to miss the flight - there was no way I could get on a plane in this state. I did not know what to do to stop the pain, and it was really just about the worst pain I've ever experienced.
Finally I ran into a shop, and saw some after sun. I could hardly speak, and I was desperate to put the stuff on, so I just threw down my dollars and didn't even wait for my change. I ran to a bathroom and slathered the stuff on.
For a few seconds, nothing happened. Then, unbelievably, the pain got worse. Then, thankfully, a few seconds later, it got better. I slathered more on. A few minutes later, it was definitely getting better. The relief I felt was huge. When it was time to board, I'd almost entirely returned to sanity, and I could contemplate 8 hours on a plane.
When I got home I googled my symptoms. It had been such a weird and awful experience, but, it turned out, far from unique. If you get burned over a large area, then sometimes, for reasons unknown, two days later you can get a sudden massive inflammatory response which causes the most horrific itch known to humanity. I'd got very lucky though - my panic-bought after sun turned out to be one of the few substances which can help - Ocean Potion instant burn relief ice. For some people, even this doesn't help, but for me, I think it saved my life. Without it I might have had to jump through a window or something.