While this does not seems like it would happen while diving, it is actually a high risk occurance. This can be casued by panic or becoing unconcious due to other health problems. Never dive if you have a lot health problems.
DCS is probably the most commonly talked about diving-related injury. When you breathe compressed air at depth, your body tissues will absorb extra nitrogen. When you resurface, if your tissues have absorbed too much nitrogen, the reduction in pressure can cause that nitrogen to create nitrogen bubbles inside your tissues. This is decompression sickness, or the bends. It causes a lot of pain and possibly death if it doesn't get treated. This can be easily prevented by watching you dive computers and acening slowly.