I've never been in more pain in my life, but its a different pain.
Its not a pain that you cry over I think coz you have to concentrate so hard on it.
Its indescribeable.
Unfortunetly though,as Westy said, the only way possible to know how it feels is to experience it your self.
It can be scary, but you just have to remember what your body is doing. Its doing what its meant to.
Its not as scary once you are there. Don't get too hung up thinking about it.