The author, Lauren Slater, of the memoir, Lying, seems to focus her story around her mother and their relationship. Some might argue that her illness takes priority as far as importance goes, but she even says that the illness may or may not even exist. She says it might just be a metaphor, a tool to help her express her tale. I feel like, if you are willing to accept it as a metaphoric tool, her epilepsy is just her way of explaining her relationship with her mother. For example, when her illness leads her to the school in Topeka, Kansas for epilepsy and she is taught how to fall properly, she says that falling the first time felt like it was a betrayal to her mother. Falling doesn't make her feel entirely wrought with guilt though. She becomes addicted to it, because it makes her feel free from her over-controlling mother.
Lauren Slater often hints like this that early on she felt like her mother was the only one who could offer her the affections and comforts that are typically lumped with the idea of a motherly figure. When her father tells her the story about the egg, for instance, she comes to realize that her mother isn't the only one who can console her and give her a sense of comfort. As a whole, I feel like she and her mother share a very dysfunctional relationship, but that she loves her mother and desperately wants to feel more connected to her. She just doesn't know how to go about forging the kind of closeness she craves with the flamboyant woman.