I saw a woman on a Sybian pass out from multiple orgasms.  That or her squirting shorted it out, I'm not sure... 

  She had been riding it for about half an hour in a restrained/forced orgasm scenario.  
But she definitely went into convulsion-type movements and was out for about 20 seconds and dazed for about 15 minutes afterwards.  We were all a little concerned, but she turned out to be fine.  Probably a combination of orgasmic activity and hyperventilating.
She came back the next weekend for another round with similar results, and then I haven't seen her in awhile.  She probably bought her own and never left the house.