Read this in wikipedia[for what it's worth to you] and wondered if training participants to not expect anything could result in this phenomenon:

Main article: Nocebo
In the opposite effect, a patient who disbelieves in a treatment may experience a worsening of symptoms. This effect, now called by analogy the "nocebo effect" (Latin nocebo = "I will harm") can be measured in the same way as the placebo effect, e.g., when members of a control group receiving an inert substance report a worsening of symptoms. The recipients of the inert substance may nullify the placebo effect intended by simply having a negative attitude towards the effectiveness of the substance prescribed, which often leads to a nocebo effect, which is not caused by the substance, but due to other factors, such as the patient's mentality towards his or her ability to get well, or even purely coincidental worsening of symptoms.[8]

http://en.wikipedia.org/wiki/Placebo...Placebo_effect

http://en.wikipedia.org/wiki/Nocebo

paula