IEEE 802.5.4-based personal area networks (PANs) are expected to play a key role for emerging mobile health applications. In this work, we evaluate network performance and reliability in the case where several PANs are forced to share the same channel. Based on extensive simulations, we show that inter-network interaction may lead to long periods of disruption, even when the average network performance is very good and the channel is only lightly loaded. We demonstrate that this is mostly due to lack of coordination between networks, rather than limitations of duty cycle or memory.