I Cannot Visualise Anything. I Close My Eyes And Only See Grey

I first became aware of my ‘condition’ as a small child. I could not get to sleep, and my father or my sister would say, “Just close your eyes, and picture sheep jumping over a wall. Count the sheep. You’ll soon go to sleep”. I tried, but told them I couldn’t see anything when I closed my eyes, just a greyness. Nobody believed me. “Don’t be silly everybody can see pictures when they close their eyes”. This was news to me, and I decided not to