I dont know what this is.

At night when I lay with my eyes closed, and am feeling tired, I try to block out as many thoughts as possible and just focus on the "Blackness".
After a small amount of time I start to see patches of colour, then they change.
They change into images, totally random and uncontrollable.
But they are crystal clear. It only lasts for about thirty seconds or so, because then I start to "think" about the images and they dissapear.

Just wondering if anyone knows what it or they are?

It's not lucid dreaming, I can do that and know what it is.