I had something like this, except for me it was my own pain I believed. But it might as well be a psychological response that can also be triggered by empathy.
When I was 10 or so me and some friends were building a forest hut, and we were putting tiles in, I was placing the tiles in order and a friend was throwing tiles close to me. As I picked up a tile he trew one right on my finger that got smashed between two tiles.
My nail was all kinds of busted, split and broken and my finger was broken at the center part. I remember walking the mile home without much of a problem, didn't even feel much pain, but when I got home to put my finger under running water, to try and get all the dirt out (impossible to clean the dirt from a busted up nail, lol, it's sticky under there.), I nearly fainted, but it was sort of inbetween being normal and fainting. Everything was very greenish suddenly in my eyes, like a fluorescent green, and all my senses were really strong, as well as the pain, that was on a totally different scale as well, like it was overruling me and my finger was in such a mess that made my stomach swirl. I keep barely keep standing. It was a really strange sensation and I could feel my heartbeat like there was a hammer continiously slamming into my finger. After I got out of that phase the pain returned to a much more normal level, the heartbeat I felt was painful but barable and the pain was okay.
