There is a great article appearing in NewScientist about the power of negative words. It it what is called the Nocebo Effect which is different than the placebo effect in one is a positive response and one is a negative response. They even mention hypnosis in the article.
The science of voodoo: When mind attacks body
There is more evidence everyday, if we pay attention, that our mind is much more in control of our body tan we CONSCIOUSLY are aware of.