You notice the inconsistency, even if you can't quite recall what the pattern was before. I've only had a few lucid dreams and I don't have great dream recall, but when I wake up at the right moment I can remember my dreams vividly, and think through the dream events with my fully conscious mind. I don't notice patterns changing that much, but I do know that text changes. For example, I've had dreams where I fell asleep while reading, then continued to read in my dream making up the story as I went. But then it gets confusing so I back up to reread a page, and the story changes.

Another common event is that people and things in my dreams can be indistinct until I pay close attention to them. Just recently I was with a woman in my dream who appeared as just a silhouette in a shadow until I really wanted to know who she was and focused on her, at which point she became perfectly clear and vibrant. That can happen to the entire setting of my dream too, and people and settings can also change as I pay attention to different parts of them.