The intensity of reported vestibular experiences by normal volunteers (n = 127, over a 4-year period) increased significantly in a step-like manner during partial sensory deprivation when the daily geomagnetic activity exceeded about 15 nT; the effect size was equivalent to a correlation of about 0.33. Post hoc analyses indicated that the geomagnetic activity during the 3-h period at the beginning of the previous sleep cycle was the single greatest contributor. The enhanced occurrences of experiences that are similar to those associated with complex partial epileptic seizures suggests that specific stimuli associated with geomagnetic activity above about 15 nT affects specific regions of the human brain; the vulnerability occurs during the subsequent 24 h. However, in non-epileptic individuals these experiences must be amplified neurocognitively by removing input from auditory and visual modalities.