I must admit that although it has felt that way to me, mine have been small -- figuring out a crossword answer, or how the evidence in a case tied together to show what happened, or why someone was behaving in a way that had seemed mysterious.
I guess this qualifies...
I like to look at the sky. Especially clouds. One day, while watching a sky full of individual puffy clouds, it was like someone suddenly flipped a switch in my head and I was now seeing the clouds, and the entire sky, as 3-dimensional objects, hovering hundreds/thousands of feet overhead, receding off into the distance. I guess I had all my life just "saw" the sky as this flat blue plane and had never really observed the depth of it all. It was, as you say, an epiphany.
It was an epiphany for me when I realised that I didn't, after all, have to have any dealings with my sister. After years of her manipulative, lying behaviour, I decided that I'd had enough. She's a totally selfish person without a shred of decency or compassion. There was a final, awful event that was the last straw and I thought "I'm done with you". And I was.
That was nearly 3 years ago. Oh, my life has been so much more serene since then.
Yeah, I had one that resulted in an entirely new career direction and really strong focus on what I wanted to do. I remember the moment it hit me, and a year or so later I had moved states, moved jobs, and started out on the path I'm still on and very satisfied with.