Hmm the worst physical pain I've experienced was probably when I simultaneously dislocated and broke my elbow joint in year four. I must have been in excruciating pain though I do not remember feeling any. I recall crawling away from the play equipment to a safe spot (which probably made the damage to my elbow so much worse) and then screaming constantly for a teacher.
I had to undergo surgery for two to three days I think and I had some metal pins inserted to help fix the positioning of the bones or something like that. The hospital wasn't too bad though.
After I returned to school, they were telling me how they could see the bone sticking out of my elbow, while I was lying on the ground. I can no longer fully straighten the arm and at one stage, it was causing me internal pain while I was punching with it. It's all good now though, as that pain hasn't returned since and my strikes are now unhindered.
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Another time, I was playing cricket and the guy hits the ball straight towards me. I was the youngest player on the team as it was under 16's I believe and I was 14 at the time. So all I could do was stop the ball with my body as my reactions were not quick enough. It ended up smashing my thumb, though it didn't break, it was very painful and put me in tears. The batsman apologized as I was escorted off the field, which was very sportsman like of him. I said it was OK in between sobs lol.
Another cricket incident involved a bad prediction on my part. I was batting and I predicted he would bowl a spin ball (he can do fast pace and spin) so in anticipation I decided to use my signature sweep shot which I was infamous for back in the day as it was the only shot I could really do, but boy did I do it well. Anyway, I swung my bat way too early (funnily enough, don't ask me how that happened, considering I thought the ball would be travelling much slower so in theory, the ball should have reached me before I had swung) and I could only watch helplessly as the cricket ball slammed into my chest and rebounded back. I fell over backwards and gasped for air. It was lucky the ball didn't rebound and smash my chin as I wasn't wearing a helmet, as it was just casual practice and I can be a bit of a daredevil at times. I was down for a good few minutes before I recovered and continued on.