the trouble of my knee...

This is, as usual, I took the bus to school for studying. I didn’t feel something wrong before I arrived our school. However, when I was ready to enter the school, I fell down beside the wall without any reason. I figured that I might be injured; because my knee hurt so much that I couldn’t walk any more. I couldn’t remember when I hurt my knee. But the truth was in front of me and I had to face it. Then, I tried all of the ways getting classroom. Nevertheless, I still could play basketball after about ten minutes. I could also jump and run as usual. I don’t know why. It’s awful when I fell down without expecting in the next four hours. I still couldn’t find the reason. I hope there will be an answer tomorrow.