1. A medical device for detecting an epilepsy event in a patient, comprising: a sensing module adapted to receive data relating to a beat sequence of the patient's heart; a NNXX processing module adapted to determine at least one NNXX value from the beat sequence of the patient's heart, and adapted to compare the at least one NNXX value to an NNXX threshold; and a communication unit adapted to provide an output indicative of at least one of an unstable brain state, a brain state indicative of an elevated probability of a seizure, a brain state indicative of an impending seizure, an aura, or a seizure based upon the comparing of the at least one NNXX value to the NNXX threshold.