You have 2 heads, 4 ears, and just one ball, and you realize it to be plain wrong. That’s because it’s unreal.
On the other hand, if this bizarre state of yours hold any truth with the reality of the world you are in (in a dream for instance), then it’s surreal.
Another example would be Alice in Wonderland. Normally, it can easily be considered unreal. However, if you somehow end up in that world, what you’d feel can be classified as surrealistic, as the things from an imaginary world are now very much real.