It could be that you were in enough pain that your brain refused to remember it. There's a certain threshold for severe pain where the brain fails to record any memory of the actual sensations -- everything else going on, even thoughts, but not that particular sensory feedback.

The stereotypical example is pregnancy, since women usually "forget" how incredibly painful it is within a fairly short time of experiencing it. I had it with both bouts of peritonitis: I remember being curled up on the bed trying to remain motionless and wanting to die, but it's almost like my brain thinks I was doing it for no reason.