I've never bumped my head that hard except maybe in an accident with a train, but when that happened I still had usable residual vision, and I can't really remember what happened anyway. Regardless I believe you experienced seeing a mechanically induced
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Despite being totally blind now, I do experience phosphenes in my right eye along with hallucinations of seeing the real world in my left eye since, although my optic nerves are completely destroyed due to glaucoma, my visual cortex is still fully functional..