I was hit by a blast of tinnitus that seems like it might have been beyond what I can normally hear (at my age, it drops off around 10Khz), so I suspect the issue is neurological in nature.
Which gets me to wondering. Can your brain produce sensations that are outside the bounds of normal perception, and how would you be able to understand them? What, for instance, would high-frequency ultraviolet light look like, in terms of how you perceive normal light?
Have you had apparent sensory experiences (of any kind) that were outside the bounds of normal and thus clearly generated by your brain, and how were you able to comprehend them?