When I realized I was dreaming, the dream looked like boiling water filmed backwards. Shapes grouping themselves into new shapes and shrinking into points. And the new shapes grouped themselves into new shapes, shrinking again. Arrangements of objects morphing into objects, starting from the edges of the visual field.
I was unable to control it, when I tried, I woke up. Maybe this becoming aware of being in a dream was part of waking up anyway, but it provided an interesting insight into the process of dreaming.