When you (You, not people in general) imagine things, do you actually see them?
Because if I try to picture, say, a cake, I can tell you exactly what it looks like, I could draw it if I wasn't such a crappy artist, but I don't actually see it. If I shut my eyes and try to imagine something, I just get black.
I always thought that was normal until I read an anecdote about this guy who said something along the lines of 'Whenever we were in kindergarden and the teacher told us to shut our eyes and imagine, i got nothing. Then one day, I finally saw something - it was dancing chicken legs.'