Words in dreams
The other night I had some pain in my chest -- not heart-related, but rather from a blow from a teenage mutant ninja niece -- which led to an interesting dream.
I don't remember the whole dream, just the very end, where I woke up with the word "pericardium" in my brain. There's nothing too peculiar about this except for one little detail: I don't remember ever hearing that word before in my life. Later in the morning I looked it up online to see if I made it up or see if it was real, and it is indeed a real word. Even cooler is that it's related to the chest/heart, where my niece hit me. Wikipedia says it is "a double-walled sac that contains the heart and the roots of the great vessels." (And no, I didn't know how to spell it the first time.)
I'm not saying that I've never heard this word before, only that I can't consciously recall hearing it before. If you had asked me if it was a real word I might have guessed yes, but the truth is I didn't know what it was. But my dreaming mind seems to know it.
I think that's cool, and crazy.