I was two dreams recently where I took drugs and felt the full effects of them. The first was codeine, I felt all the positive effects without the side effects. The second was a sedative that doesn't exist in real life, I snorted a line of it and it felt like getting hit with an elephant tranquiliser. That gives me pretty solid personal evidence that we can utilise the placebo effect to change ones state. The question is how to do it consciously though. And is it easier to do it in the dream state than real life.