It was particularly horrible because it was a freaky eye nightmare, one of my major fears (not entirely unrelated to the state of my retinas, also probably connected to a lot of eye background exams I had ever since birth). I blogged about it at the time. The flashback was triggered by looking in the mirror in the same way I had looked in the mirror in the dream. It didn't last long, but for a moment that dream image from my memory was more vivid than reality, and it was disorienting because I had forgotten the dream after waking.

Actually this theme that I look into a mirror an my eyes are weird or changed or injured is a recurrent nightmare for me. A more recent, and more detailed and gross example of the same I this post, though thankfully I had no flashbacks to that one once I was oriented, but was only freaked out after waking from it. (the second link is flocked, but you should have access)