Head-Mounted displays, while providing unprecedented immersiveness and engagement in interaction, can substantially add mental workload and visual strain on users. Being a novel technology, users often do not know what to expect and therefore accept visual stress as being state of the art. Assessing visual discomfort is currently possible through questionnaires and interviews that interrupt the interaction and provide only subjective feedback. Electroencephalography (EEG) can provide insights about the visual discomfort and workload of HMDs. We evaluate the use of a consumer-grade Brain Computer Interface for estimating visual discomfort in HMD usage in a study with 24 participants. Our results show that the usage of a BCI to detect uncomfortable viewing conditions is possible with a certainty of 83% in our study. Further the results give insights on the usage of BCIs in order to increase the detection certainty by reducing costs for the hardware. This can pave the way for designing adaptive virtual reality experiences that consider user visual fatigue without disrupting immersiveness.