Using Internet of Things (IoT) in the health domain is one of the most promising approaches which offer a ubiquitous healthcare where sensors are used, in real time, for constant monitoring of patient's symptoms and needs wherever he is. Wireless body area network (WBAN) is a highly suitable communication tool for the medical IoT devices. However, the conception of WBAN applications is still a challenging job that should take into consideration many technical requirements such as network lifetime, security level, network throughput and data criticality and prioritization. As a consequence, a trade-off between security effectiveness, energy efficiency, and QoS requirements can be perceived as a major performance objective. In this paper, we propose a stochastic game to balance the tradeoff between network performance and security level while taking into account the context dynamics. Simulation results show that the proposed approach can achieve an acceptable security level and is more efficient than benchmark algorithms in terms of network lifetime and throughput.