Once the penny finally dropped it was mind-melting. It's been three or four years now since I realized my experience is unusual, and I'm _still_ discovering ways it impacts how I experience life differently than most.
A memorable moment was telling a friend who already knew I was aphantasiac that I struggle with mental arithmetic, and being completely lost when he replied, "oh, right, because you can't make the numbers dance in your head."
I said, "what?"
After a minute of confusion, he was finally able to get across that when he does mental math, he actually writes the problem in his mind's eye and does it on virtual paper.
I think that was the day I first realized that it really is a handicap in many ways.
OTOH, an upside is that I've never had to wish for "brain bleach". I didn't understand that phrase at all until the past year or three. I occasionally think that aphantasiacs should be preferentially chosen for high-trauma-exposure jobs, like EMT - we simply can't retain those horrible moments.
I'm not on HN super-regularly, but I'd be happy to take a few minutes to answer questions the next time I check in.