Systems, devices, and methods for adjusting functionality of an implantable medical device based on posture are disclosed. In some instances, a method for operating a leadless cardiac pacemaker implanted into a patient, where the patient has two or more predefined behavioral states, may include detecting a change in the behavioral state of the patient, and in response, changing a sampling rate of a sensor signal generated by a sensor of the leadless cardiac pacemaker. In some embodiments, the method may further include using the sampled sensor signal to determine an updated pacing rate of the leadless cardiac pacemaker and providing pacing to the patient at the updated pacing rate.