I disagree with the premise. I don't believe that more bad things happen in previous lives, but that the bad experiences are what affect us the most, so that when things come up to be healed, they're the bad things. We don't need healing from good things, so they go unnoticed.
I have no opinion as to whether people die suddenly more often when they're undergoing past life therapy, and I'd like to see studies comparing the rate of death while past life therapy vs just regular treatment of medical issues.
The provisional belief that previous life stuff causes present medical issues is an additional obfuscating datum.