Here is what you do, keep making it up. When the information comes up, it enters your imagination, and you use your imagination to put it into words, so it can seem like you are making it up. Don't fight it, and don't start saying this is not working, because chances are it is working.
What I like to do is talk about that after the end of the session. After you open your eyes, I will ask you, do you think you made that up, and then we have a conversation about it. And here is something else. What about dreams? Do you just make up your dreams, or where do those come from?
In a dream your conscious mind is asleep, so if purple pigs fly by carrying blue umbrellas, you do not question it, you just let the dream unfold. In hypnosis your conscious mind is somewhere in the background, observing, and it may find these images incredible. Pigs are not purple, it says, they do not fly, and especially not with blue umbrellas. Yet when a dream ends and you look at the imagery, there is always meaning in it. So say the first thing that comes to mind, and save the analysis for after the session.