The name "hypnosis" comes from the Greek word for sleep — which is misleading. Hypnosis isn't sleep, even though trance can sometimes feel similar.
In trance, your conscious mind is usually still present, just in the background — your subconscious moves into the foreground instead. That's exactly what makes hypnosis useful: many habits, fears and reaction patterns live in the subconscious and barely budge through pure thinking. In trance, that part becomes easier to reach.
I work with suggestions rather than commands, and deliberately go one level below the actual symptom — to the cause. For more on the science behind it, see Hypnosis Science.