Aims: We study the ionized gas emission from the large scale shock region of Stephan's Quintet (SQ). Methods: We carried out integral field unit (IFU) optical spectroscopy on three pointings in and near the SQ shock. We used Potsdam MultiAperture Spectrometer (PMAS) on the 3.5 m Calar Alto telescope to obtain measures of emission lines that provide insight into physical properties of the gas. Severe blending of Hα and [Nii]λ6548, 6583 Å emission lines in many spaxels required the assumption of at least two kinematical components to extract fluxes for the individual lines. Results: The main results from our study include (a) detection of discrete emission features in the new intruder velocity range 5400-6000 km s-1 showing properties consistent with Hii regions, (b) detection of a low-velocity component spanning the range 5800-6300 km s-1 with properties resembling a solar-metallicity shocked gas and (c) detection of a high-velocity component at ≈6600 km s-1 with properties consistent with those of a low-metallicity shocked gas. Conclusions: The two shocked components are interpreted as products of a collision between NGC 7318b new intruder and a debris field in its path. This has given rise to a complex structure of ionized gas where several components with different kinematical and physical properties coexist, although part of the original interstellar medium (ISM) associated with NGC 7318b is still present and remains unaltered. Our observations suggest that the low-velocity ionized component might have existed before the new intruder collision and could be associated with the NW-LV Hi component. The high-velocity ionized component might fill the gap between the Hi complexes observed in SQ-A and NGC 7319's tidal filament (NW-HV, Arc-N and Arc-S in Williams et al. 2002, AJ, 123, 2417). Based on observations taken at the 3.5 m telescope at Calar Alto Observatory.Tables 1-5, Figs. 12-19 and Appendix A are available in electronic form at http://www.aanda.org