When I was about 3 I was diagnosed with a condition called Chiari Malformation. Basically my cerebrospinal fluid flow was being blocked by a displacement of my brain stem through the hole in the skull where the spine enters. If it was not corrected by widening the hole and taking off the back half of my first vertebra, i would soon become paralyzed below the neck. and so i had surgery, leaving me with a 4-5 inch scar and a terror of becoming paralyzed that lasts to this day, because the surgery could become undone by neck/head trauma.