That wouldn't happen. Hallucinations such as this are caused by chemical imbalances in the brain. The least I would suspect in the way of treatment for such hallucinations would be a prescription for Lithium.
I just said it did for this scenario. You've been told there is nothing wrong. No chemical imbalances; no mind-altering substances... but you've had a vision....
GOODNESS! You seem to live in a very tiny universe. In any case, in my experience as a clinical psychologist, you are simply wrong.
Not all "visions" are hallucinations by any means. Visions can occur for a variety of reasons. Mental/neural dysfunction is just one. Emotional dysfunction is just one. Your statement comes more out of your world view than out of the body of truth about experiential reality.
Some "experts" think we know enough to make all kinds of outlandish statements. But there's lots we still don't know. There's a lot of "experts" trying to prove that ALL NDExperiences are merely chemical artifacts of traumatized brains. But there are many examples of seeing objects and aspects of settings unknown and inaccessible to any of the bodies involved at the original time.
There are many anecdotal examples of people having visions of loved ones being safe or dying which later turn out to be exactly accurate. Chemical happenstance in the brain is a GROSSLY INADEQUATE explanation. Accepting such an explanation takes more faith in chance chaotic firings of neurons than I could begin to have.
I find myself beginning to feel sadder for you. I understand the need to have reality in tidy little boxes. But it's kind of sad to observe someone who REALLY seems to think/live as though they've SUCCESSFULLY so packaged reality.