1. A non-transitory computer readable program storage unit encoded with instructions that, when executed by a medical system, perform a method for detecting a seizure, comprising: receiving via one or more processors of the medical system a heart rate of a patient; calculating via the one or more processors of the medical system a change in the heart rate; selecting via the one or more processors of the medical system, in response to a calculated change in the heart rate, at least one of a maximal heart rate, a reserve heart rate, an activity heart rate, and a resting heart rate; detecting via the one or more processors of the medical system the seizure based on the change in the heart rate reaching a threshold value in reference to the selected at least one of the maximal heart rate, the reserve heart rate, the activity heart rate, and the resting heart rate; and initiating via the one or more processors a responsive action where the responsive action is a delivering of a therapy, in response to the detection.