In this paper, performance analysis of hybrid localization based on radio-frequency (RF) and inertial measurement unit (IMU) measurements for a single wireless capsule endoscopy (WCE) traveling the gastrointestinal tract is studied. Specifically, the multiple body-mounted sensors are considered which are located on the front and back of a patient's medical jacket and form the uniform rectangular arrays (URAs). With the aim of locating the WCE, two types of RF measurements, namely time-of-arrival (TOA) and direction-of-arrival (DOA), are estimated from the received signals at the URAs transmitted by the WCE, which are integrated with the IMU acceleration measurements via the standard extended Kalman filter. Here, a posterior Cram,r-Rao Bound (PCRB) of the proposed TOA/DOA and IMU-based hybrid localization is derived as fundamental limits on squared position error, where the accuracies of TOA and DOA measurements are entailed by means of CRB to account for their dependency on the environmental parameters, while the accuracies of the IMU measurements are addressed with the acceleration measurement error standard deviation. Numerical results are provided, sustained by simulations which verify the millimeter accuracy of the TOA/DOA and IMU-based hybrid localization within the regulation of medical implant communication services and the exactness of the PCRB.