I wouldn't call a dream an illusion, I'd call it a different perspective.

Afterall, all dreams or imaginations must be based on some kind of fact for inspiration.

After humans have finished rushing around trying to rule to world before 40 years of age, all they have are dreams that slow the mind down enough to see the truth.

I'm also reminded of a track by incubus (New Skin, on the science album):

Originally posted by Incubus
Untill the 20th century, reality was everything humans could touch, see, smell and hear.
Since the initial publication of the chartered electromagnetic spectrum, humans have learned that what they can touch, see, smell and hear, is less than one millionth of reality.