A question about what is illusion

There is the illusion that we are separate beings. We are not.

There is the illusion of time. Time is not.

All of these illusions occur because of any attempts to fix the image. Life is a moving thing. Everything changes yet we are ever eternal. The difference between illusion or reality is in the ability to be transparent to every change and keep filled with the certainty of each moment along the way. Let's just say that the answer you received is not the gospel of what is really going on. We are given the concept of illusion so that we can recognize the changes and that these changes are in themselves malleable through the influence of mind.
In this sense your fears are illusions because a change of mind brings the rays of light which shine through the fears, dissipating them, making them transparent and leaving in their place the certainty of each moment. There and only there is the reality in the changing movement of the eternal as we reflect (enter vantage point upon vantage point) on these changes causing indeed the very changes we are reflecting upon.
That is why in an instant a person's life can undergo dramatic changes as your mind changes, adjusts and recognizes now the eternal being that is becoming. What exists is I AM in and through everything. When your identity rests there every thing is possible. Using this analogy the creator rests within the soul of the created. Every attempt to find the creator without is meaningless. It's like looking for your glasses when they are on top of your head. You take it with you wherever you go.