Illusion means that one knows the unreality of a thing only when it disappears.

Illusion means that one knows the unreality of a thing only when it disappears. When one knows these three states are continually appearing and disappearing, he may perceive its unreality. As one goes deeper inquiry he becomes aware the consciousness is in the process of changing every moment, to moment. 

The experience of the Birth, life, death world is within the waking or dream. It is connected with the body of the waking or dream. Waking or dream comes and goes. But which sees the birth, life, death and the world of the waking or dream as a whole is the consciousness, the innermost self. The innermost self, is immortal. –FORMLESS PATH