When I graduated from high school, we had a hypnotist come to the grad night at our school (grad night=big party for grads). He hypnotized groups of 10 or so people at a time, though you could tell about half the people weren't getting hypnotized at all while the other half were completely in to it. A friend of mine was in one of the groups, and was hypnotized to think that he was Shania Twain. They put a ton of makeup on him and a wig and a little skirt and he lip synched "Man! I Feel Like a Woman"--it was priceless!
Afterward I asked him about it and he said he could still conciously think (like "wait...what am I doing?") but it was more like it was in the back of his head and the hypnotist's suggestions were way more dominant.