The ability to assess a user's emotional reaction from biometrics has applications in personalization, recommendation, and enhancing user experiences, among other areas. Unfortunately, understanding the connection between biometric signals and user reactions has previously focused on black box techniques that are opaque to the underlying physiology of the user. In this paper, we explore a novel user study connecting biometric reaction to external stimuli and changes in the user's autonomic nervous system. Specifically, we focus on two competing responses, namely the sympathetic and parasympathetic nervous system, and how differing activations are related to different user responses. Our experiments demonstrate how prior psychophysiological research distinguishing this activation can be replicated using biometric data collected from wearables. The insights from this work have applications in better understanding emotional state from biometric sensors.