My Response: This is a phenomenon that happens when a person begins to be shaped by a particular emotion. This is a sign of emotional expression; the emotion itself having no form. So the letters that made it possible for you to describe something as emotions begin to disappear and you no longer see them.
It could also be the other way around, when a person who is reading a Kabbalistic book can suddenly see additional words appear that are not written in the text. These are not miracles because the texts that are written by Kabbalists are multilayered. If you are lucky and achieve a level like this, you will see many additional words that arose in the thoughts of the author.
From the Kabbalah Lesson in Russian 7/24/16