Negative Placebos

If you do any research on the placebo effect, your mind will be blown at how powerful the human mind is. But, I wonder if too much of our time is spent on considering the power of "positive" placebos?

What about negative placebos? What about when we get tricked into thinking we feel bad?

If a doctor can give me sugar pills that make my "allergy headaches" go away, perhaps the times that I'm feeling bad, I really don't?