I've been pretty lucky, but:
Once I was playing with model rocket engine powder, broke open the cardboard tube, dumped it out into a pile. Got my hand a little too close when I lit it and powder burned my fingers. Some of my nails were brown and burnt. I thought I really f'd my self, but it healed up fine. It hurt like a bitch for the rest of the day though, was better when I woke up. Felt like I had my hand in a flame all day.
I passed a kidney stone, but it could have been worse.
I had bruised or hurt one of my ribs banging into something, and later it resulted in some kinda air pocket popping when I shifted funny when I was laying back in my computer chair. I didn't really figure out what happened until many years later. My lung collapsed and I had trouble breathing and it hurt to move. I was standing, holding myself up on the back of a chair. I was in incredible pain and I couldn't stand up. This was like 13-14 years ago. My parents helped me to the couch and I passed out and fell to the floor. I remember them being like "Wade?! Wade?!" as everything went black and my hearing got all funky. Then I came too and got to the couch and laid there in pain. Was still sore the next day. Why the hell we didn't call for an ambulence or something is beyond me. I didn't even go see a doctor. I just recovered from it, which is normal. Most people recover without help, but you should have a doctor check on it. Based on the symptoms and the situation I'm 99% sure this is what happened, my lung collapsed, then as the pressure in my chest normalized it went back to normal.
What happens is when these air pockets burst, like a bubble, it screws up the pressure in your chest and your lung can collapse, or partially collapse. It was probalby just a partial collapse.
I've stubbed my toe many times, and that always hurts like a mother. :)