Optical resonators have been extensively investigated during the last century. Still some important revisions of their understanding are recently emerged in the framework on non-Hermitian theories, leading to counterintuitive effects, such as complex modal volume and Fano-like local density of states. We experimentally demonstrate all these predictions in cavities on photonic crystal slabs with relatively low optical loss. Near-field hyperspectral imaging via quantum dot photoluminescence is proved to be a direct tool for detecting the counterintuitive effects of non-Hermitian theories. The experimental results fully agree with the predictions.