1. A method of selective data retention in an implantable medical device, the method comprising: sensing a neurological event; creating a data record of the neurological event; determining a severity level of the neurological event; storing the data record in a data structure containing a plurality of data records, the plurality of data records representing information about a plurality of neurological events; determining a priority index for the plurality of data records based on severity levels of the determined neurological events; and selectively replacing an existing data record in the data structure with a newer data record that has a higher priority index than the existing data record.