In the Afterword of her novel, Lauren Slater writes that, "Lying is a book of narrative truth, a book in which I am more interested in using invention to get to the heart of things than I am in documenting actual life occurrences." Slater goes on to talk about even her epilepsy, the main focus of the entire story, was only a metaphor. It was merely a clever metaphor, twisted from small shreds of her actual reality in order to convey a much more important truth.
To Slater, narrative truth is everything. It is her way of expressing her unstable and troubled life as she felt it while living it, not as it technically happened. The emotional impact of Slater's life, as she experienced it, is the most important type of reality to her. It takes weight over the factual truth of events. That is the reality Slater portrays in her novel. It's the reality that she felt she had to tell, like she was almost compelled to tell others about. Slater even speaks of feeling relief at having finally managed to find a way to express it in epilepsy. In the end, I loved this book even more, because of the truly artistic way she managed to use epilepsy as a metaphor to cleanly and crisply explain so many things about her life.