Urban ninja - back blocked

So today I passed by in the office and there was Gino. He was going to a ridicolous martial art training, so I shown him some basic movements, as he seemed to be lacking even the basics of the art. But something in my back started hurting, and in order not to depress Gino, I pretended that I was fine. Now I'm at home, blocked in bed by back pain. There's something cursed about that guy.