Disclosed herein are methods, systems, and apparatus for detecting an epilepsy event in a patient using a medical device. The medical device is capable of determining an occurring epilepsy event, for example a seizure or an increased risk of a seizure. The determination is performed by determining at least one nonlinear analysis parameter associated with the beat sequence of the patient's heart. The medical device may then take a responsive action, such as warning, logging the time of the seizure, computing and storing one or more seizure severity indices, and treating the epilepsy event.