When my father was young, about 16 years old, he went to a park at night to see his friends. To go there, he had to walk up a street in complete darkness, no light poles, no flash light, no moon light, nothing. As he walked half the street something in his head switched. Without any warning, his vision changed to a black, white and grey vision. He could see everything on the street with stunning details, even the end of it. My father always had good vision (no glasses) but nothing exceptional (just above average I would say). He told me this a long time ago and still talks about it sometimes. He said that a specialist described it as a lost ability of the brain and the eye. He also said that it could have been a hormone that created a chemical reaction with the retina of the eyes. I would like to know what you think of this experience and what may have happened.
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"The true mind can weather all lies and illusions without being lost. The true heart can touch the poison of hatred without being harmed. From beginningless time, darkness thrives in the void, but always yields to purifying light."
To me it sounds like as you said something explainable. I do know that there are people who can see sounds and hear colors due to something in the brain.