The rapid technological convergence between Internet of Things (IoT), Wireless Body Area Networks (WBANs) and cloud computing have contributed to the emergence of e-healthcare, significantly improving the quality of medical care. In particular, patient-centric health monitoring plays a vital role in e-healthcare service, involving a set of important operations ranging from medical data collection and aggregation, data transmission and segregation, to data analytics. This survey paper firstly presents an architectural framework to describe the entire monitoring life cycle and highlight the essential service components. More detailed discussions are then devoted to data collection at patient side, which we argue that it serves as fundamental basis in achieving robust, efficient, and secure health monitoring. Finally, a set of design challenges is particularly analyzed for developing high quality and secure patient-centric monitoring schemes, along with some potential solutions.