The name "hypnosis" comes from the Greek word for sleep — which is misleading. Hypnosis isn't sleep, even though trance can sometimes feel similar.
What happens to your mind in trance
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. With an anxiety, for example, you often know perfectly well that the danger isn't real — and your body still reacts as if it were. That's because the reaction isn't stored in the conscious, analytical part of your mind, but in a part that works faster and more automatically. In trance, that part becomes easier to reach.
How I actually work in a session
I work with suggestions rather than commands. A command ("You will no longer feel afraid from now on") gets checked by the conscious mind immediately and usually rejected, because it sounds too absolute and unbelievable. A suggestion ("Notice how this is slowly starting to shift") leaves room your unconscious can fill in itself. In doing that, I deliberately go one level below the actual symptom — to the cause, not just the visible behavior.
One thing matters here: you're responsive and conscious throughout the whole session. It isn't a state where you're "gone" — it's a state of focused, inward attention, comparable to the moment on a long drive where you're so lost in thought that you barely consciously registered the last few kilometers. Trance isn't exotic; it's a natural state you already experience regularly in everyday life — we just use it deliberately.
For more on the science behind it, see Hypnosis Science.