Understanding own body performance and factors influencing it is a challenge, especially because the complex environments we live in influence this performance, and, when relying only on our subjective, momentary observations and feelings, we may easily draw wrong conclusions. Fortunately, nowadays we can access devices and services for self-tracking of own body and its performance in context. In this paper I present an example of own idiographic study of self-tracking of heart rate (HR) and daily life activities along a period of 3 consecutive months. I present the study challenges, as well as I discuss the lessons learned from self-tracking for self-management of my health. I discuss my aim of generalization of such a study approach towards a larger population.