Do you see elaborate unrelated to the real world pictures when you close your eyes?
I used to get these as a kid in the classroom all the time, later in life at uni lectures too. Usually they come when trying to concentrate on something. Fortunately they are just weird and not disturbing. I wish I had the skills to paint or 3D model all of them, they are so detailed and imaginative, out of this world.
Do you see them too, Bernd?
And no, I never tried drugs or alcohol. From googling around these hallucinations seem typical for someone on LSD.