The public opinion and the scientific community incorrectly believe that the English term "lunatic" was originally related only to insanity, but it also referred to epileptic people. The aim of this article is to clarify the original meaning of the English word "lunatic" by analyzing the evolution of the relationship between psychiatric and neurological diseases and by pointing out the influence of the moon in the history of medicine, in popular traditions, and in English literature. The article also contains a detailed and accurate review of the modern scientific literature on the relationship between moon and epilepsy/psychiatric disorders.