There's something I don't understand and I'm wondering if someone can help me figure it out; When you go to the Sleeping worlds I understand why you see Neku, Joshua, Sam, and the other characters but what I don't get is why do you see Mickey, Minnie, Donald, Goofy, and Pete in the sleeping worlds since they're wide awake in the Realm of Light (especially Mickey he appears two times!!)

The Mickey, Donald and Goofy that were seen in the sleeping worlds were derived from the memories of the sleeping worlds from when those three were present in the Country of the Musketeers and when Mickey was at Yen Sid's Tower.

I hope that that makes sense to you.

Edited November 14, 201311 yr by Varnish

Basically, the only reason they should up because that world was in sleep and that's where Mickey , Donald, and goofy originated (one of the places) that's why they end up in the sleeping worlds

So were they just memories that took on a physical form or because they were all wide awake did the Realm of Sleep create copies of them??

So were they just memories that took on a physical form or because they were all wide awake did the Realm of Sleep create copies of them??

They were derived from the memories of the worlds.

As I see it, those worlds are asleep and those who lived on that world that particular time heart is still connected to that world, so that part of their heart it asleep along with that world. At least that's how I see it

Essentially, you're going back in time. 

This scene does a somewhat ok job of explaining it, though it's not fantastic:

 

 

The Sleeping Worlds are worlds that, of course, have fallen to darkness at one point or another.  They rest for the time, waiting to return to the light.  While doing so, they 'dream' about occurrences within them; memories from their past.  People familiar to the real world (Such as Jiminy, along with Mickey and others) aren't actually there.  They are simply the world remembering them being there.  I suppose, as Kaweebo said it, visiting the sleeping worlds is almost like going back in time, but I don't believe that is the case.

Edited November 14, 201311 yr by Keyblader

Like the others said,the Sleeping Worlds are the worlds that have been falling into darkness,and dream about their memories from the past and took form from it...

Thanks for clarifying guys I think I pretty much get it now