I had a VERY hard opening about 5 weeks ago.  Didn't fully lose consciousness, but was unresponsive for some unknown amount of time.  No serious injuries--very painful stress fracture of the sternum kept me on Vicoden for 3 weeks.
  Sabre 170, loaded at 1:1.  I was playing with a new Audible, so was on my belly, stable, waiting on pull time.  I always pack for myself (except this time).  It was my 6th jump of the day and was tired, so used a packer at the DZ who is experienced  and trusted (I'm not blaming the packer).
  Being new to the sport, this is my first injury and, frankly, it spooked me.  I don't want another opening like that one!
  I've been told the following:
 1.  Sabres have a reputation for opening hard on occasion (is this true?)
 2.  Perhaps it was a simple packing error (if so, what exactly would cause a hard opening)
 3.  Maybe it was my body position at pull time (but I was on my belly, waiting on pull time)
  Just trying to figure out what happened and how I can avoid it again...
  Al